Because ~99% of internet companies seem to either fail or be acquired, it's the nature of the beast. Only a handful of companies (like you mentioned Oracle, Google, Apple, Amazon) live long enough for a founder to even stay there.
Actually I think it's usually the case where a company is founded by 2 or 3 really passionate people. Typically, there's one who's passion stays with the company for the test of times. With Microsoft, it was Bill Gates with Paul Allen leaving. With Apple, it was Steve Jobs with Wozniak no longer there. With Twitter, it Dorsey staying (after having been pushed out) with Evan leaving.
Apple first tried to push developers to the web. It was because of the hacking community that apps got popular and they opened up the iPhone OS (now iOS).
Mobile apps are great for small and quick functional tasks. It's not a great interface to do incredibly complicated actions unless they can be done at the press of a button, minimal typing or by a swipe.
I agree there's a lot of crud out there but I'd like to see where Adam Conrad has solved world hunger, ended climate change or stopped wars. He calls everyone else out. Where's his contribution to solving HUGE problems? :)
I think small apps by small teams have to start from somewhere. However, we probably don't need any more fart or lighter apps.