> Why do people react to C++ this way and not other languages?

Probably because stuff like boost::mpl (and so many awful half-implementations of it) exists.

Sadly, if there's a perceived use for a C++ feature, it will be used, no matter how convoluted it is. This is a specific case of a general method for adding state to constexpr, which might be considered useful... I wouldn't be shocked to see this used in the future.