I hated when doing math homework and they didn't give me the answer sheet. If I could do an integral and verify if it's correct or not, I could either quickly learn from my mistake, or keep doing integrals with added confidence. Which is how I learned the best. Gatekeeping it because someone might use the answers wrong felt weird, you still had to show your work.
Yeah. I also felt it largely went at odds with the entire concept of flashcards. Which... are among the most effective tools that I did not take advantage of in grade school.
I imagine the thought process is that even when one must show their work, having a sneak peak at the answer allows a lazier student to work the problem forwards and backwards hoping to fudge through the middle plausibly well.