It's a subtle stab at Debian-based distributions, where pip and venv are only available as optional, non-default packages. (I think Debian really wants people to use apt to install things.)
That said, I think debian users should lean heavily on the apt versions of any python modules. I will usually install as many modules with apt as possible and then use `python3 -m venv --system-site-packages` to have access to them. That way there are usually very few packages I need to compile/install myself. Seems like a pretty good balance.
pip is another beast: it's not included in the stdlib, but installed when you install Python with the ensurepip script. Debian just don't run the script.