Exactly this.

In uni I got offered internships as part of the course, to write my Master's thesis.

An engineering firm in Aerospace offered me a job doing something with airplanes. Pretty interesting, but paid £12K/yr, which really isn't much money, even for a student.

I kept my mouth shut (uni wanted us to take whatever came) and got offered a job at a major chip manufacturer, but in marketing. Also interesting, £15K/yr. I took it and learned a bunch about that business.

I went to visit a friend in London who'd gotten an internship working at an investment bank. £38K/yr.

What do you suppose I applied to when I graduated? It wasn't engineering or marketing.

As things happened, I'm still an engineer. I just make algorithms to move money around, and that's also got nerd value, since there's interesting problems in financial trading as well. I've literally has days where I made more money for myself than I would have gotten in a whole year at either of the other careers. I also ran into people who'd dumped those careers to work in finance, because the incentive is so strong (colleague directly told me he saw his boss's payslip, then decided to leave).

I agree with this. It's easy to get caught up in a very binary "in it for the money" vs "doing what you love" mindset, but I think the reality is a balance of both. Money is actually quite great and I am willing to compromise a little bit in my day job in order to receive more money. At the same time, there are some jobs I simply do not want to do, even if they may be higher paid than what I'm doing now.

This is a very reasonable take. As you say, you can become interested in any complex systems to try and solve problems, so the main differentiator can become money. The issue I was pointing to is nobody else was pointing out that same context, they were solely about money. Not solving worthwhile problems. Not developing skill sets. Just the paycheck