Probably because of the extremely high performance requirements. There's a lot of packets going through a 10Gbit interface and if you run some Python code for each of them you're gonna choke the machine.
This does not seem to be an argument. Any language (maybe with some restriction) could be compiled to the appropriate byte code/assembly.
FYI, it is very easy to add a users group on Debian/Ubuntu. Having used both systems, I like to have a users group and a group per user. It gives much more fine grained control over things.
This. I am an OpenSUSE user and for me it is the best distro overall (polished, great infrastructure: BuildService,