Retrofit in object form

I have an MVVM program that uses Retrofit and Hilt
I have two questions:

1. Why the most examples the Retrofit was created in object form instead of class form?
2. Why we shouldn't implements (inheritance) the AppModule from Retrofit to make a limitation for accessing the Retrofit directly?

My personal experience leads me to write it that way, but I have never seen something like it. I want to know about expert programmers' opinions on problems in my suggested way.

Retrofit class:

open class BaseApi protected constructor(){

private fun createBuilder(baseUrl : String): Retrofit {
    val okHttpClient = OkHttpClient.Builder()
        .connectTimeout(15, TimeUnit.SECONDS)
        .build()
    return Retrofit.Builder()
        .baseUrl(baseUrl)
        .addConverterFactory(GsonConverterFactory.create())
        .client(okHttpClient)
        .build()
}

protected fun getWeatherService(): WeatherService {
    val weatherServiceBaseAddress = "https://api.weatherapi.com/"
    return createBuilder(weatherServiceBaseAddress).create(WeatherService::class.java)
 }
}  

AppModule:

@Module
@InstallIn(SingletonComponent::class)
class AppModule : BaseApi() {

    @Singleton
    @Provides
    fun weatherServiceProvider() = getWeatherService()
}