Why do freckles and blemishes keep appearing?

It’s frustrating because even though I’m taking good care of my freckles and blemishes, they seem to keep appearing.
I know it's because of UV rays, but I've heard that even if you apply sunscreen well, it's difficult to completely prevent freckles and blemishes.
I think it is harder to manage because there is also a hormonal influence.
I also see a lot of talk saying that it is more realistic to keep freckles and blemishes light rather than trying to get rid of them completely.
I want to know the cause of why this keeps happening and figure out how to manage it. I would appreciate advice from those with experience.