This is assuming you have the correct version of python installed, right? What if you were on CentOS and the python version is 2.6? Or on Alpine and you simply didn't have python at all?
What if you download a binary and a dynamic library is missing? (This is what happens with GHC on Alpine. Binaries will expect glibc. Packages fix this problem, but they also fix the Python problems.)
Another example: I recently wanted to run IDA on Arch Linux, but there are no 32-bit Qt5 packages. Compiling Qt5 is more painful than installing Python.
Another example: I recently wanted to run IDA on Arch Linux, but there are no 32-bit Qt5 packages. Compiling Qt5 is more painful than installing Python.