Smartphones saw rapid growth in China at the same time as mega-apps formed. The tech giants that built these mega-apps also acquired many consumer services that used to be independent companies and integrated them into the mega-app over time. Then out of the interest to compete with each other, these tech giants kept making their own mega-app larger in order to capture more user activity within their ecosystem of services. The emergence of mega-apps in China was not the consumer's choice.
We already have "everything apps" - it's called a browser. I would indeed be missing that if we didn't already have it.
I can also imagine how people might find it convenient to have essentially browser, messaging and payment combined into a single thing (essentially WeChat) they can use instead of a variety of separate apps/accounts.
But I'm also sceptical anyone can make that happen in democratic capitalist countries without insane amounts of investment.
But outside web-browsers, I'm not sure it is anything anyone wants - like you imply, in China it's probably handy, because it is a reliable route into all the services that are blessed by the CCP, which means you avoid running into firewalls & thought police.
Yes, multiple things can be combined, but if it works, probably just coincidence.