I think there is some cognitive load involved in context switching between many apps and websites, managing separate accounts and passwords with each, knowing their UI differences, etc.

Opening chats to 5 recipients and ordering stuff from them with free form text is a lot lower friction than installing 5 apps or navigating to 5 websites, meeting their password complexity requirements, reentering addresses and CC numbers, etc.

It's not good news for freedom or the open web, but it probably does lower friction for users to give you money.