A classic and very frustrating problem! You're not really doing anything wrong, in fact, if you're getting females you're doing almost everything right, you just aren't the first person to crab there this season. Crabs are crabs, the males and females are attracted to anything different from a bait/depth/bottom type perspective. The problem is just that the area you've been crabbing has been heavily pressured by either recreational, or maybe commercial crabbers. Most of the males have already been caught for the season. My best advice is keep trying new places until you find some male keepers. If you have a favorite popular spot, make sure to get there early in the season.