1. Work at a company that runs some ancient version of CentOS or something.
2. The system package manager doesn't have anything newer than Python 3.6.
3. Official binaries from python.org print an inscrutable error about the glibc version when you try to run them.
4. Building Python from source requires some new system dependencies, takes forever, and then produces an even less scrutable error about a missing header file.
5. Googling that error leads to a ./configure flag that works around the issue, which upstream GCC fixed in 2017.
6. Success?
If you haven't seen that error #3 before, or dealt with "manylinux" build environments, you've dodged an entire world of pain. The same goes for scripting installs on Windows, and for the part of that page that's talking about "limiting the CPU instructions that can be used" :')