For a new project, teams can decide whether to use Go, but there are many millions of lines of existing Python servers out there.

Not to mention that there are differences in ecosystem, familiarity, and ergonomics that may make a team want to stick with Python.

“Just use Go” is not really actionable advice in most cases.

Libraries. I use both languages, and a survey of what libraries are available is part of picking an implementation language when starting a greenfield project.

It's a tradeoff. Go programs are extremely slow at starting up for example.