Why do some people major in stuff such as Physics, Music, Anthropology, etc when their grades are good enough for medicine? (I am not talking about countries in America where you have to do pre-Med/Law courses, but countries where you must do these degrees as an undergraduate.)

Anyone with common sense can tell you that the job markets for people with these majors are shit, and if you go to grad school, the job market isn't necessarily any better. You can try to transfer back into Law or Medicine, but it will be very competitive.

Sure someone will end up with a stable job which pays nicely, but chances are it will not be you. Work is not meant to be fun, every job has its own terrible aspects, money is important and a person can always learn to love his job.