Both the PIN and the app feel like terrible ideas. The gym I go to uses NFC wristbands, for the turnstiles but also for the lockers.

You can actually do this, as a fob, but you have to buy one from a vending machine in the gym. Remembering the pin is easier.

That’s also really bad. Who wants to carry a wristband around everywhere? Keychain barcode tag works fine.

What do you mean everywhere? You just throw it into your gym bag.

Many gyms let you rent lockers by the month, so you can store your gym bag there and be able to drop by without necessarily having planned on it when you left home. Can’t do that if you have to carry a wristband around to get in.

I've never been to a PureGym; if you guys use a PIN-pad to enter does that mean they're like those unattended 24/7 gyms?

...or if they do have an attendant there, why can't they let you in with a friendly greeting like they used to in some imagined past?

They're 24/7. There are usually some staff onsite during the day, but all the entry/exit stuff is always through the automated gates.