Clubs in the 80s, 90s, and I'd say even 2000s before the recession, absolutely had higher standards for their dancers. This is generally speaking, of course - there are still some top tier clubs with high standards. But back in the day, the dancers really had to look like showgirls, have few or no visible tattoos, always have their hair and nails done, be fit, etc.
There are many factors, but I do think the recession had a huge and negative impact in dancer quality. Clubs were struggling because the economy was struggling, girls became more desperate (extras became more rampant), and more "average" looking girls turned to stripping to make money. Are the clubs going to be super picky at that point, when girls are literally paying THEM to work there?
The payment issues (house fee / tipout) are another thing that lowered the standards. In the 80s and 90s, the clubs paid an hourly wage to the dancers (at my mom's main club she got $17/hr plus whatever tips she took home... another older dancer I worked with worked at a smaller club back in the day and told me she got $14/hr).
So, if the club is employing you and putting you on a payroll, naturally they are going to be more selective. Now that it's the opposite, where girls pay the clubs, talent has dropped.
Those are just some reasons, but there are plenty more. Also, Americans just keep getting fatter in general. So basically today, any "average" girl can be a stripper at a decent club, whereas a few decades ago, you basically had to look like you could be in Playboy.