Which SDKs do you use that are C++?
I use Keil, IAR, Renesas's compiler, XM8/16/32 from Microchip, and GCC.
Which do you use?
One of the main features of C++, its object-oriented stuff, is built on top of constructors and destructors -- aka dynamic memory allocation. This sort of thing is not desirable on deeply embedded systems due to resource constraints and the very real spectre of heap fragmentation -- embedded stuff tends to rely on static memory allocation done at compile time or system startup.
C++ isn't quite as portable as C -- Not just the compilers which never quite supported the same combinations of features -- even if you just stuck with the ISO-ratified features -- but the language runtime, standard [template] library, and headers are far larger with various implementations including plenty of mis-features and quirks. All of this meant that it was quite common for C++ code to not even compile with a different toolchain -- especially when templates were used -- and even if it did compile, it might not actually function correctly.
If you restricted yourself to avoid the problematic areas of C++ (eg not using templates or dynamic allocations) you'll end up with a language that is basically C. So why not just use C? :)