They need to "ping" you meaning when you run past a villager and they make the "!!!" and try to talk to you. Try having nothing in your pockets and go use your wet suit and sit in the water for 10-15 minutes. Very high chance you'll get a villager to ping you. If the villager doesn't recommend a PW, rinse and repeat the wet suit trick till they do.
In simpler words; time. It takes time to get PWP's of different varieties to be requested. You need to wait for them to ping you and there is always a small chance that when they do, they want to request a PWP.
The wetsuit method always works for me; one thing tho-- before you go swimming (sitting in water), have your pocket full of stuff villagers won't ask to buy (like flowers, sea-shells) so they won't ask you to buy, trade, or take things off of them. Helps a little to increase the chance of villagers requesting PWP instead of them asking to buy/trade/etc.. they can still ask you to change their greeting/catchphrase/new nickname or ask you to visit their houses, etc...
Also remember that you only get one PWP request a day. Unless you TT often, you have to be patient.