Because 95% of the time high school work doesn't transfer to the college level even if you do semesters at De Anza. You're back to scratch unless you go to flagship in-state, and even then you can only transfer up to a certain amount (at my undergrad it was up to Calc 2 - several people I know took Calc 3 in the same institution in high school but had to take it again).
Even if a college didn't want to transfer the credits for Calc 3, I'm surprised that they wouldn't allow you to skip the course. Also, for your friends, if they took a class at the same institution... doesn't that mean they got a repeat? Strange.
I also wouldn't generalize these things to people who occupy university posts, as they probably had interesting trajectories.
yes
> as they probably had interesting trajectories.
Not every physics professor went to a top school and published groundbreaking research.
I do want to emphasize that taking Calc 3 again is one class out of dozens you need to graduate.
The gains become clear depending on the degree to which you know what you want, and especially if you're thinking about graduate programs.
1. Calculus in some sense is somewhat disorganized, and it sucks that it's a gateway to more math in the US. By finishing Calculus early you can move on to the math you wanted to learn, such as Linear Algebra.
2. University students may have to spend about a year learning Calculus. That's a long time, and to some people they'd rather spend their money better by learning something else or graduating early.
3. If you're thinking about graduate studies in something technical such as Econ or Stats, then you'll probably want at least Analysis. The problem is that in the grand scheme of things, even Analysis does not leave you very prepared to do things, it just makes you prepared to learn more, so you may want to get ahead of this problem.