after sommany years the raincoats get too boring

For most of sec with a condom isn't the same, it just isn't. And if we are undetectable meaning there is zero risk of infecting someone else then why not? As for someone on PrEP there is the risk of infection albeit a small one. It is possible to be infected by someone with a strain that is resistant to Truvada. But the risk is much much lower then without. And I didn't use protection before PrEP was available so I'm pretty sure they probably do it for the same reason as I did.