OS's have limits on when you can do some stuff - for example allocating/deleting stuff in an interrupt handler (and the associated code that interacts with it)

OS's have limits on when you can do some stuff - for example allocating/deleting stuff in an interrupt handler (and the associated code that interacts with it) - mostly you code around this by just not doing it if you possibly can - but C++ might be doing this behind your back. And when you do need to do it you will likely use a special allocator and associated heap that knows how to interact safely with ISRs - just doing a 'new' without being able to say "where" and "how" is a problem. And then you have to be able to delete/free it the correct way too. Essentially it means that an important chunk of the language and standard library are off limits in an important part of an OS, and lots of evil bugs are available to people new to the game who just blindly new stuff (or let the compiler do it behind their back)