Here you confuse 'most apps' with Twitter and Facebook. Most apps
are crud apps; there are some apps that are not. Those apps are the most used, but they are not most apps by app count.
Only people here on hn seem to think that everyone is slinging k8s and 1000 layers of microservices to build the most complex things on earth; the rest is earning their paycheck by building some forms in php.
Sadly many here are overengineering crud apps and then somehow making them out to be something more than crud apps because somewhere in the future they might be (probably not); as in, you can build 'a twitter' in 1 weekend and it will even probably handle good volume of users ( more than Twitter did at startup; it was often down or very slow) etc if you just take postgres with php on a few $/mo server. It is a crud app at that time (the flow for these user authored posts is built into every trivial and complex framework these days). Also it will most likely be bankrupt in a few months as that is what happens to startups; I rather spend money on building the business first and then scaling the tech; which is exactly what Twitter did. On hn it seems a lot of people work backward in that regard but that probably has also something to do with being a techie and VC interest in scalable tech.