The guy who created a monolithic kernel in the 90s thinks C++ sucks
C++ is a horrible language. It’s made more horrible by the fact that a lot of substandard programmers use it, to the point where it’s much much easier to generate total and utter crap with it. Quite frankly, even if the choice of C were to do nothing but keep the C++ programmers out, that in itself would be a huge reason to use C.
In general, I'd say that anybody who designs his kernel modules for C++ is either (a) looking for problems (b) a C++ bigot that can't see what he is writing is really just C anyway (c) was given an assignment in CS class to do so.