I don't think that's true that people want 1 thing that does it all. They certainly want one bill, that I'll grant, but that's not exactly the same thing.
People want an ecosystem that is easy to adapt to, and more specifically they want _the ecosystem they're familiar with_. In a past life with software support, when it came to large/enterprise customers, the biggest pushback/fights had nothing to do with features or price, but with a few stubborn IT Managers/Administrators who were used to another product and didn't want to change.
UI/UX should have a common 'language' for lack of better words between them with a spin on it that still makes it unique for the program. We already see this with desktop OSes and mobile; if I right-click on any common desktop OS, I know I get a contextual menu on an object, if I swipe or tap on mobile likely something will happen, etc. Users mostly get this except for a small subset and can use a lot of apps; the app ecosystem on mobile more or less demonstrates this.
What Meta is doing with WhatsApp isn't about the one app for all, it's just they have a huge user base that isn't bringing in money and likely they see this as a cardinal sin _not to monetize_ WhatsApp somehow. They likely look at WeChat and go "wait you can make money like that?" and are desperately trying to figure out how to get themselves there. I have not been in the US for a long time so I don't know how people there will adopt to Meta-Money or whatever Meta ends up calling it. For the EU countries I've lived in, I'm not as confident people will want to be doing that with Meta at least when Apple/Google Pay exist and work pretty alright and banking apps already handling fast direct payments without needing an SV intermediary.