There would be a lot of friction to do it with fiat currency. I presume that would mean Visa cards which not everyone would have, there would be fees associated with that too, and Visa's have a 90 chargeback policy. Maybe Paypal is easier but even less will have access to that. The biggest point though is that bitcoin/lightning doesn't require permission from anyone to use, and no one can be censored from using it 😎 paypal would probably suspend all of us for suspicious activity.
We're also just a bunch of bitcoiners too, lol.
It's not baked into nostr though. Someone can make clients that use whatever currency they want.