RaspBerry doesn't find pip3

sudo apt-get install python3-pip

This should install pip3 for managing Python3 libraries. If you're using rasbian that is.
python-pip is for Python2 (as of 2019-09-09) if you need that too.

pip and python are two separate entities. There for installing one doesn't necessarily mean the other will be installed.

Some good documentation on the matter can be found at raspberrypi.org

And others have asked the same question on the official forums.

Just remember, most "safe" distro's tend to default to Python2 for their LTS platforms pre 2020. Meaning you will have to essentially add python3-<lib> (the 3 being the crucial element here) to all your installations. Otherwise you'll most likely get the Python2 equivilant of the library/tool for as long as Python2 is the default python environment in your distro. Like in this case.

Again, I'm using Arch Linux ARM for the most part, so I'm not to familiar with debian/ubuntu/etc distro's for the RPi platform. But that package should be called about the same as in Arch :)