Originally, I disliked C++ because it was poorly supported across platforms. You had this level of standard support on one platform, but only that level of standard support on that other platform. From STL to every other useful library. It made things difficult to port. But that was long ago, before I stopped using C++. Things may have changed since then. Platforms have become fewer and far in between at least. C is widely implemented on all platforms and in fact, most platforms have large chunks implemented in C.

The other thing is about class-based languages. They are great for implementing hierarchies of concepts, like GUI toolkits and a few other things. But, they do promote bulk and it's not rare to have a lot of object thrashing. That's not specific to C++, though.

Third, system-level library are often exclusively exposed via C libraries. Core things like BSD sockets, POSIX threads, memory management. Yes, you can wrap them in C++ or use C++-based libraries that add sugar on top, but more often than not you end up wondering "why don't I use the system APIs directly?" You often feel like you have to jump through unnecessary hoops when you don't.

Just my opinion, of course. I would use C++ if there was a good reason for any particular job. It is just not my natural inclination.