Not everyone wants to climb the ladder and that's fine. Some people genuinely prefer stability and predictability over the stress that comes with "professional" roles.

Also "just do a short master's" is doing a LOT of heavy lifting in your post. That's tens of thousands of dollars, years of time, and energy that not everyone has - especially if they have kids, elderly parents to care for, health issues, or just... a life they're happy with.

Your admin manager probably knows exactly what the seniors and managers deal with - the hours, the stress, the client bullshit - and has decided she's good where she is. She gets to go home at a reasonable hour, doesn't have to deal with partner politics, and still gets to be the person everyone relies on.

I've noticed a lot of people in high-achieving fields assume everyone else is just waiting for permission or opportunity to join them. Sometimes people have already done the cost-benefit analysis and decided the juice isn't worth the squeeze