I am not convinced it is just that. PayPal also refuses to do business with online gambling which is an industry with low fraud levels (in the early poker days they were high, but that was a long time ago). Thankfully there are a bunch pf credit card processors who know how good customers online casinos are and most banks are fine too, so that industry is not deplatformed.
I would imagine gambling sites would get a lot of chargebacks. Consider a user that transfers money to the site and loses it all. That user might initiate a chargeback to get their money back.
Most of the online gambling operators in New Jersey take PayPal, though you usually have to use either a bank account linked with ACH or a balance you already have in PayPal.