When you already lost your frenulum, the only thing that keeps the skin bunched up against the glans is the prepuce. The prepuce works like a rubber band. When you roll your skin forward, it squeezes together by itself. When you roll back, it has a pretty hard limit in width it allows. When pretty limited, the cause of swellings.
It can take a long time for the hard maximum width to adjust to the width of the shaft. You can see it as a slightly dented zone when rolled back. I have seen a nice picture illustrating this here, some time ago. It is the upper outside part of the foreskin. It is also the area that is the last to wrinkle. First, when you progress, you get lower shaft wrinkles. But then the prepuce rubber band keeps squeezing forward. Keeping the skin from fully and freely spreading over the shaft.
Some guys are lucky and already have a prepuce maximum width that matches the shaft diameter. But most are not so lucky. Especially with thicker skin. They keep having what's also know as a goose neck for a long time. You can help progressing by stretching the tip of the prepuce with two or four fingers. Sleeping with a bare glans helps as night time erections will help the stretching. With penis activities you can try to always keep the foreskin back as far as possible as that is stretching as well. Still it can take a pretty long time for the whole penis skin to have the same diameter. Possible reason why the prepuce is such a tough cookie to crack might be that the whole idea is it is supposed to cover the glans after heavy penis work to recover faster and have a break. Sort of like a "shields up" thing. But no medical or science I ever encountered to support that theory.