Or you know, maybe it takes 3 days in order to provide protections for buyers and sellers. Paypal sees wide use because it's generally considered a relatively safe and easy payment option that's widely accepted among small online businesses.
Credit cards similarly have buyer protections in place. At least in the US, there's long been a federal law that prevents people from being held liable for more than $50 in fraudulent charges, or $0 if the card is reported stolen. And most credit cards even cover the $50 for their users, resulting in $0 fraud liability. Many cards will provide additional purchase protections as well.
If someone gains access to a person's crypto wallet, there are no protections in place, and the transfers are generally irreversible.