Payments. The sticky part of "everything" app is the payments platform. With a payments platform you have a internal "funded" ecosystem. Anybody who can not take payments from the "everything" app has a incentive to get inside so they can get paid. In many countries, the "everything" app contains, what in the US would be called, a bank.

This is basically illegal in the USA. US Banks are extremely stringently regulated to the point where many international banks do not even want to take US customers because that would subject them to US laws about banks. That is how insanely challenging it is for literal banks with decades of past and current experience to manage the regulations. "Move fast and break things" would get "Go directly to jail, do not pass go". Even money transmitter licenses like Paypal and Venmo are extremely challenging. And even those companies try really hard to make sure they do not get classified as a bank.

Trying to graft on a social platform onto a bank or a money transmitter would make the entire social platform subject to bank/money transmitter business restrictions which is almost certainly doomed legally. It is not like these companies do not know to add payments, it is just so insanely hard that even the 900 pound gorillas do not want to mess with Godzilla.