This is the case for most of the thrift stores I'm able to hit without going way out of my way. It's the flip side of LA thrift abundance. It makes it a different game, too - it's not hard to find, for instance, a Brooks suit in good shape for $60. The trick is to find a brand they're not onto or to find the thrifts that haven't caught on.
At the end of the day, though, it's hard to complain. These are charitable organizations and they deserve to make as much for their cause as they reasonably can. Of course, I'm a hobbyist and a half-assed one at that; I'm sure I'd feel different if this were a serious part of my income, and I'm sure flippers have been on balance way better for thrift shops than not.