Pip is a third party project, so if you'd like to pursue this please open an issue on the pip issue tracker at https://github.com/pypa/pip/issues.

Anyway, pip installs links named the way it does so that you can be (more) sure that you're invoking the correct pip.  'pip3.6' will invoke the pip installed with python3.6, 'pip3' will (or at least should) invoke the pip installed with whatever 'python3' points to, and 'pip' will point to whatever 'python' points to.  When installed in a Python 3 venv, pip also installs a 'pip' link to 'pip3', just as there's also a 'python' link to 'python3'.  In 2.7, pip is also installed as 'pip2.7' and 'pip2' along with 'pip'; again mirroring the version tags on the interpreter links.