PayPal originally was convenient as it saved you from filling in card details each time and also allowed sending payments for private transactions using only an email.

Since then Apple Pay/Google pay/browser wallets have taken a big chunk of its fast checkout advantage

And mobile banking apps/instant transfer have taken out chunks of the private transactions, and more so as consumer to consumer transactions often had the parties using PayPal gift mode to avoid fees but that also then had zero protection.

The 2020’s is much more crowded than 1990’s and 2020’s decades

Also its was its partnership with eBay that made it dominant and eBay no longer promote PayPal as preferred payment method.