Unfortunately all the ides I tried make it non trivial to write extensions. I program nearly 9 hours a day and using a tool that prevents automation of common tasks is suboptimal.
To clarify, with plugins such as ctags, rtags and YouCompleteMe. I would never be able to write large C++ programs in vanilla vim. Maaaybe plain C, but definitely not C++.
1. The IDE cannot deduce the type within templates, and more code is moving to templates (e.g. generic lambdas in C++14)
2. Code is often read outside of IDEs: code review, search engines, etc.
3. Should C++ become a language that requires an IDE to work effectively, like Java? Probably not.