I remember reading somewhere that brief fly use is pretty closely tied to age, almost everyone who uses the scrunch-down method is under a certain age, while most men over a certain age use the fly.
When I wore briefs (I think I stopped in high school) I used the scrunch down method. When I switched to boxers, I used the fly most of the time. Now that I wear boxer-briefs, sometimes I use scrunch-down, sometimes I use the fly.
Interesting tidbit - flies are still incorporated into most men’s underwear because flyless underwear was seen as feminine, no different from panties. I kinda agree, flyless underwear does look kinda funny to me.