If they could make it elsewhere, they would.
I don’t expect this to be a popular take here, and most replies will be NAXALT fallacies, but in aggregate it’s the truth. Sorry, your retired CEO physics teacher who you loved was not a representative sample.
"and then a bunch" is somewhat misleading. They in fact take easier and fewer classes in the subjects that they are studying for, but they have to take extra classes on education, which afaik are not that hard to pass. Getting a "Lehramt" degree is much easier than getting the regular degree in a subject, which is why many people that are simply not good enough for the real thing do it.
Also we have a teacher shortage and more and more teachers are not in fact people that received an education you usually have to get as a teacher, but are just regular people with either a degree in the subject they are teaching or a degree in almost anything (depends on how desperate the schools are and what subjects they are hiring for).