Not trying to defend the choice of `git checkout` over `git switch` (and `git restore`) but they were introduced in v2.23 of Git [0], which was released about 5 years ago [1]. If you take a look at their help pages, they still include a warning that says
> THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOR MAY CHANGE.
Granted, it has been in there for basically as long as the command(s) existed [2] and after 5 years perhaps it might be time to no longer call it experimental.
Still, it does seem like `git checkout` might be a bit more backwards compatible (and also reflective of the time when this website was originally created).