Who knows. Every company is different, has different customer bases, different histories, different technologies. Maybe they signed a deal with paypal where they get lower fees, maybe they integrated it in a time when it made more sense then now (e.g. before apple pay and google pay were so prevalent), maybe they outsource their payment to a processor that just supports it.

I don't know the details of any of these places, I was just giving a reason why a company may not implement a particular payment processor. It's based on a balance of factors, not just a simple "support X get more paying customers."