C++11 vs C++14/C++17/C++20 is not python2 vs python3. Because of the emphasis on backwards compatibility, you can often just recompile your C++11 project with the new version of the standard and everything should just work. Backwards compatability also means that the newer versions are only as "complex" as the features you choose to use.
The tricky part of this is that if your project is a library, you're not just opting into having to update your own toolchain, but also that of all your users. This means that a lot of library developers will err on the side of not updating their minimum version, which in turn means application developers don't have as much pressure to update either. This isn't specific to C++ by any means, but I think it does pop up a bit more in this space due to the fact that a lot of developers prefer to just use the default toolchain of their system, so forcing downstream users to update their toolchain could be viewed as a bit more of a maintenance burden.
