I think it's probably actually just because they want to support users who wish to have a "minimal" python installation. Python is used internally by the system and many applications, but that doesn't mean that features like venv are necessary for them. It does make sense not to install them unless needed.

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.

venv is actually a module of the stdlib in Python 3, so you can use python -m venv even on debian. You are confusing with virtualenv, which is a different tool than venv with the same purpose.

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.