As an Arch Linux user I am forced to be very particular about the programs I use on my computer because everything on my system is something that I put there, but people like me are of course a minority when it comes to worldwide computer users. For most people there is really only one program on their computer that matters, the browser. This is how Chromebooks are able to exist, Google Chrome is really the only program on a Chromebook and the other programs are just slightly modified web applications that work almost exactly the same as the version that runs in the browser. While from the perspective of an educated user this is terrible, from Google's business perspective this may be one of the smartest things they've ever done, sell cheap computers only capable of running your most popular program that already has thousands of developers working on it.
Now of course Chromebooks aren't the only type of computer and Google Chrome certainly isn't the only browser every program that can run within Google Chrome can run on any relevant browser. Word processors run in the browser, so does Zoom, and even VS Code can run within a web browser, of course doing this is almost never better than running these same programs outside your browser, but you can do it if you want to. You can almost think of your browser as an operating system built on top of your existing operating system (although that's not quite the case).
Flash is probably best remembered for the games that it allowed people to play, there were lots of sites hosting them and while most were garbage and all of them were a waste of time but there were a few that were fun, plus when you consider the fact that the target demographic for these things was children under the age of ten you realize that quality was never a big concern anyways, many of these kids were completely satisfied as long as they could attribute their button pressing to something "productive" and vaguely interesting.