Everyone is using llama.cpp because we reject the idea of giving up on system libraries like nix does. That kind of tomfoolery (at least in the desktop context) is only required when you use software projects that use libraries/languages which break forwards compatibility every 3 years.
If you just write straight c++ (without c++xx, or anything like it) you can compile the code on machines from decades ago if you want.
Huh, I was proficient in Rust before "properly" learning C++, so maybe that accounts for it, but I didn't realize C++11 was controversial. Is it just move semantics, or are there some library things that are hard to implement?
And maybe that "C++" is now basically a bunch of different incompatible languages instead of just 1 language, depending on what "xx" is (11, 14, 17, 20, 23, etc).
In my experience, C++03 code works just fine without changes on a C++11 and C++14 compilers, so no, it's not at all like Python 2/3. The few features that were ripped out were exactly the stuff that pretty much no-one was using for good reasons (e.g. throw-specifications).
