Property without setter cannot be assigned to, but other one without can

I'm seeing some really strange behavior (probably something obvious I'm missing) in my C# code.

The following causes an error on the TableName property. "A property without setter or inaccessible setter cannot be assigned to".

public class MyEntity
    {
        public IList<MyRow> Rows { get; }

        public string TableName { get; }
    }

Usage:

var myEntity = new MyEntity
                    {
                        Rows = { myRow },
                        TableName = "SomeString"
                    };

The error goes away if I add a set; to the TableName property. How come the Rows property doesn't need one as well?