I don't have acne, but why do I keep getting red marks?

The breakouts themselves have decreased a lot compared to before, but the problem is that red marks always linger for a long time after the acne goes away. Even if just a small pimple pops up and subsides, the mark remains for weeks, so it makes my skin look unsightly and upsetting.

I hardly ever touch or squeeze the marks, so I don't understand why they last so long. I'm curious if it's because my skin is thin or if its regeneration is slow.

For those of you who have tried products like Vitamin C serum or regenerating cream, did you see any results? Or I'm wondering if time is just the answer for these red marks. Please share any tips you have on how to manage them!