It's due to how the puzzles are generated. Positions that have a jump in centipawn evaluation are used as puzzles. If you're under 1500 then stick to the basics. Analyze all your games. The only way to improve is to practice and study.
Instead the main approach is to just mix new problems into the pool and let users try them. If there are no plausible alternatives, everyone gets the right move and the problem quickly becomes too low-rated to be shown to most players. If there are tempting alternatives and the correct solution is hard to calculate, it will become high-rated and only shown to stronger users.