Why can't nested generic types be inferred?

Given the following classes...

public abstract class FooBase<TBar> where TBar : BarBase{}
public abstract class BarBase{}
public class Bar1 : BarBase{}
public class Foo1 : FooBase<Bar1> {}

...and the following method...

public TBar DoSomething<TFoo, TBar>(TFoo theFoo)
    where TFoo : FooBase<TBar>
    where TBar : BarBase
{
    return default(TBar);
}

Why can't the following line of code imply the return type?

Bar1 myBar = DoSomething(new Foo1());

Instead I have to specify the generic types like this...

Bar1 myBar = DoSomething<Foo1, Bar1>(new Foo1());