It's surprisingly common for PhD programs to restrict outside activities, although that's probably field dependent. Not the same as the OPs story but I know multiple neuroscience programs where if you are receiving any funding from the University you are barred from working other jobs. There were always a couple students that snuck around and bartended on the side anyway, but it was crazy to me they had to actively hide this from the school - and not even just their PIs but also random program admins. I never understood why programs think they should be able to control students outside of working hours, but it doesn't stop most people. One of these programs gets over 500 applications a year for ~20 spots.
> I never understood why programs think they should be able to control students outside of working hours
They think this for the same reasons all employers think this; employment is a watered down form of ownership.
Advancement up the social hierarchy allows one to abuse the people below them. As near as I can tell from my own experience: money and control are the things you receive as rewards.
Because when you are a grad student there really aren't "working hours". Your project is supposed what you are devoting all of your effort to. In part this is due to your advisor wanting results and papers, but these also help you.
Maybe this helps students in the direct sense of modern academic career advancement, but I think it makes grad school a much more negative experience than it needs to be, and more broadly is a detriment to academic culture. I've encountered students that were forbidden from taking even a single class after they met (the very light) degree requirements, students who were not allowed to TA or volunteer mentor, students who had to sneak around just to finish analysis for a project they did with their previous lab, etc. This structure kills creativity and collaboration, and it results in a lot of graduates that have bare minimum teaching experience and no idea how to advise. Shocker that we've ended up with so many PIs that are really shitty managers!
A top neuro program in a major city will pay ~40K per year (and this is high relative to many other sciences). The rest of the compensation is health insurance and a meaningless "tuition" credit in order to register for a full "courseload" of research. Even at 40 hours per week that is shit compensation relative to what most of the students could be making elsewhere. The thesis project takes place over ~5 years, which is more than enough time to produce very good output on normal working hours. If students want to make their project their whole life fine, but as it stands there is way too much pressure coming from the top to do so, with minimal real benefits actually reaching the students.
> It's surprisingly common for PhD programs to restrict outside activities, although that's probably field dependent.
It's also supervisor-dependent! After I was formally accepted into a post-grad program, I was talking to my supervisor, my then-recent engagement slipped into the conversation and h - a senior bachelor and resident grump - did not approve of me getting married. He thought it would be distraction; I very much doubt that it was departmental policy, but my future research hinged on his whims.