It's legal verbiage to cover their asses. They don't mind porn in the slightest. They don't mind anything except perhaps CSAM.
They're taking payments from people, so they mind about what Mastercard and/or VISA will care about if they notice it.
You're agreeing with me, right? On the internet it's hard to tell. Yeah, this is about money and power.
Mastercard and Visa, like age verification, child protection, voter ID, cellphone registration, paying for bandwidth, and a few more tactics, have been a side-door that authoritarians and authorities of various types have been using to bring more of the internet under control. Globally, not limited to any one particular place - I can think of examples from every continent.
... well, except Antarctica.

Kunlun and McMurdo Stations have
wild parties together. (Especially the Marvel nerds who, like me, said 'There's an Antarctic Base named from Iron Fist?')