Web server to deny the request because the query string is too long

I tried to hit the route /home/login on my asp.net web app, but the query string auto generated to be very long!!

I read articles about making changes in web.config and trying to change default values of query string length but I want to know why is it happening at first place??

Here is my Home Controller (I had commented the non useful part)

namespace Data_Grid.Controllers
{
    public class HomeController : Controller
    {
        //public HomeController(
        //  ILogger<HomeController> logger,
        //  IConfiguration configuration,
        //  UserManager<IdentityUser> userManager,
        //  SignInManager<IdentityUser> signInManager
        //)
        //{
        //    _userManager = userManager;
        //    _signInManager = signInManager;
        //    _logger = logger;
        //    _configuration = configuration;
        //    con.ConnectionString = _configuration.GetConnectionString("OEM_US_SQL_CORL");
        //}


        //SqlCommand com = new SqlCommand();
        //SqlDataReader dr;
        //SqlConnection con = new SqlConnection();
        //List<TableData> proactivemonitoring_missing_pvr_orders_errors = new List<TableData>();

        //private readonly ILogger<HomeController> _logger;
        //private readonly IConfiguration _configuration;

        //private readonly UserManager<IdentityUser> _userManager;
        //private readonly SignInManager<IdentityUser> _signInManager;


        public IActionResult Index()
        {
            FetchData();
            return View(proactivemonitoring_missing_pvr_orders_errors);
        }


        //-------------------------------------------------------------------------------------------
        // /Home/Login
        //-------------------------------------------------------------------------------------------
        [Authorize]
        public IActionResult Login()
        {
            return View();
        }

        //[HttpPost]
        //public async Task <IActionResult> Login(string username, string password)
        //{
        //    //login functionality
        //    var user  = await _userManager.FindByNameAsync(username); 
        //    if(user != null)
        //    {
        //        var signInResult = await _signInManager.PasswordSignInAsync(user, password, false, false);

        //        if (signInResult.Succeeded)
        //        {
        //            return RedirectToAction("Index");
        //        }
        //        else
        //        {
        //            return RedirectToAction("Index");
        //        }
        //    }
        //    else
        //    {
        //        return RedirectToAction("Index");
        //    }
        //}

        //-------------------------------------------------------------------------------------------
        // /Home/Register
        //-------------------------------------------------------------------------------------------
        public IActionResult Register()
        {
            return View();
        }

        //[HttpPost]
        //public async Task <IActionResult> Register(string username, string password)
        //{
        //    //Register functionality
        //    var user = new IdentityUser
        //    {
        //        UserName = username,
        //        Email = "",
        //    };

        //    var result = await _userManager.CreateAsync(user, password);

        //    if (result.Succeeded)
        //    {
        //        var signInResult = await _signInManager.PasswordSignInAsync(user, password, false, false);

        //        if (signInResult.Succeeded)
        //        {
        //            return RedirectToAction("Index");
        //        }
        //        else
        //        {
        //            return RedirectToAction("Index");
        //        }
        //        //sign user here 
        //    }
        //    return RedirectToAction("Index");
        //}

        //public async Task<IActionResult> Logout()
        //{
        //    await _signInManager.SignOutAsync();
        //    return RedirectToAction("Login");
        //}

            
        //private void FetchData()
        //{
        //    if(proactivemonitoring_missing_pvr_orders_errors.Count > 0)
        //    {
        //        proactivemonitoring_missing_pvr_orders_errors.Clear();
        //    }
        //    try
        //    {
        //        con.Open();
        //        com.Connection = con;
        //        com.CommandText = "SELECT * FROM ProActiveMonitoring_Missing_PVR_Orders where isICMSent='No'";
        //        dr = com.ExecuteReader();
        //        while (dr.Read())
        //        {
        //            proactivemonitoring_missing_pvr_orders_errors.Add(new TableData() {
        //                CustomerNbr = dr["CustomerNbr"].ToString()
        //            ,
        //                CustomerName = dr["CustomerName"].ToString()
        //            ,
        //                MSOrderNumber = dr["MSOrderNumber"].ToString()
        //            ,
        //                Quantity = dr["Quantity"].ToString()
        //            ,
        //                PromoQuantity = dr["PromoQuantity"].ToString()
        //            ,
        //                QtyDiff = dr["QtyDiff"].ToString()
        //            ,
        //                NetAmount = dr["NetAmount"].ToString()
        //            ,
        //                PromoNetAmount = dr["PromoNetAmount"].ToString()
        //            ,
        //                AmtDiff = dr["AmtDiff"].ToString()
        //            ,
        //                ExtendedAmount = dr["ExtendedAmount"].ToString()
        //            ,
        //                PromoExtendedAmount = dr["PromoExtendedAmount"].ToString()
        //            ,
        //                IsICMSent = dr["IsICMSent"].ToString()
        //            });
        //        }
        //        con.Close();
        //    }
        //    catch (Exception ex)
        //    {
        //        throw ex;
        //    }
        //}

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
        }
    }
}

Other routes like /Home/Register and /Home/Index are working absolutely fine!! Then why this?