They could have done all those things but still retained backwards compatibility. Consider how WPF was introduced as a complete replacement for WinForms. This didn't mean WinForms stopped working! You can run both under the same .net version and you can use most recent C# version (and all other libraries) with both.
It is great that MS delivered a ground-up rewrite of ASP.NET. There is no reason this should cause the old ASP.NET framework to stop working. They could exist in parallel just like WPF and WinForms - one for new code, one for legacy code. Old libraries should just keep working by default.
It is great that MS delivered a ground-up rewrite of ASP.NET. There is no reason this should cause the old ASP.NET framework to stop working. They could exist in parallel just like WPF and WinForms - one for new code, one for legacy code. Old libraries should just keep working by default.