[dellamonica]

It can get really tricky: using reflection you could read a string from any input and create a generic type instantiation that never happens in the source code. How would the code for that type be present in an AOT scenario?

There are also several optimizations that can be made in AOT compiled code that are not allowed when you enable unrestricted reflection or dynamically loading code. As an example, suppose an interface is implemented by just one type in your code. If you AOT compile it, the compiler can safely assume that all calls to methods on that interface actually go to that single type implementing it, thus it can replace interface dispatches with direct calls.