WeChat Pay (Tencent) and AliPay (Alibaba) are both huge indeed. I have no clue how much cash they bring in, tho I would expect Visa and Mastercard make way more, but they are widely used, especially the former (WeChat is quite the super-app in China)

The reason why they would want this, in my interpretation anyway, is that there is a lot of product fit to have payments on WhatsApp. The app is widely used outside NA as the communication channel, namely by lots of SMBs that actively use it (see [0], that app is solely used for business owners as it's rather useless for a regular WA user). The monetizing opportunities on WA are deeply tied to SMBs, basically you should be able to operate a business on WA in which case you shouldn't have to go off-app once you get to payment, removing payment-middlemen is probably in the interest of all three parties involved too. Payments are necessary to enable "business over chat", you can also see them working on this with Click-to-WhatsApp/Click-to-Messenger ads and the acquisition of Kustomer. This is all valid for Messenger as well but I think that's more of a TBD, it's yet to prove itself popular for that kind of usage, tho there is a good fit for Marketplace and to compete with Venmo. It's also implemented on Facebook and Instagram for their respective Shops platforms, I don't think there's more to it than that for those.

Just like Apple Pay is a rounding error[1], I wouldn't bet on payments being a significant cash cow, not any time soon anyway, considering Facebook's approach to monetization. IMO it's more about deepening the moat and broadening the utility of the apps, especially WhatsApp as it tries to become something of a communication+commerce+payments super-app for Asia/Latam/Africa (credit cards and phone numbers would be rough to displace in North America and Europe, I sure as hell wouldn't bet on FB overtaking those). A Signal or a Telegram could take over a chatting app (if it somehow reaches, like, 2B people), it would be much harder (as if it wasn't hard enough to beat such a network effect) to take over a chatting app with a built-in suite of features for businesses and a user base that gets accustomed to commercial use of said app.

I could also be entirely wrong, I'm just an idiot that tries to follow the company.

0: https://www.statista.com/statistics/1276030/whatsapp-busines...

1: https://www.statista.com/statistics/1060577/apple-pay-revenu...

I figured I'd point out why you're (probably) being downvoted in case you don't understand. The problem of payments is obvious, it's literally ancient. It's a ridiculous and naive statement that anyone would have to look at WeChat to realize it's a valuable problem to solve.