A few points on this:
- How and when would you know a subject doesn't click? In my case German (my first language) and English sucked for roughly 8 years. I ended school with A in both and was the only student in my school without a single mistake in my exam.
- School gives you good grades if you managed to learn the topics at hand. Being able to learn what is needed or what you are bad at — not what you want and are good at is a skill in itself that can be important in life. I'd argue unless you are an exceptional genius (unlike 99,999% of pupils) you gain more from pulling through than you would if you called yourself a genius and focused on a single topic. Schools goal is to educate the majority
- pupils (and often also their parents) are utterly unable to judge which bits of school will be essential to their later life. I had many collegues who utterly hated every second of a multitude of subjects, only to years later tell me how glad they are now to have had been subjected to it (which brings me back to my first point)
We could (and should!) argue on how school works as a system of grades, teachers and pupils — ideally teachers would motivate students to become curious about and proficient in subjects without the motivation of good or the threat of bad grades. But if my experience as an educator at the university levels (without grades in mh case) shows one thing it is that those first semester students who are really able to judge what will be useful to them later on are not many. Many of them are more like the dog in the meme: "Only stick, no take" — they want to be able to do the cool thing without knowing what is needed to do the cool thing.