PayPal originally took off as it was convenient and fast, saving you from filling in card details each time and it also allowed sending payments for private transactions using only an email address

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 then had zero protection.

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

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