> but then most C++ seems to use a C-style cast

If C++ programmers do not use modern safety features, that's really their fault. C-style pointer casts should be flagged in code review.

> but that it becomes even less safe by adding a C-style cast.

At least in C++ there is a safer option. If you really want to be on the safe side, you can even to a dynamic_cast (assuming your code base allows RTTI).

> It is also not clear what is gained by forcing programmers to add a cast.

I think the point is to make it explicit and stand out.