Quite the opposite. Your sizes are more popular so they fly off the thrift racks. This leaves the unpopular stuff on the racks and many thrift stores don't do a great job of cycling out old product.
If you want to find great second hand clothes, figure out when the shops put out new product and shop on those days.
If you want to find great second hand clothes, figure out when the shops put out new product and shop on those days.