There is a radical idea discovered in the 70s, that you can just buy computers and run your own code on your own machines. Rumour has it that some still practice this ancient art.
If you're happy with the experience of using computers in the 1970s and 1980s, you are of course free to continue using computers that way. Meanwhile, all the people who want to build a "quick web app" are building on top of an enormous tech stack which they don't understand. Your application will be affected by everything from the way that your TCP packets get routed around the world, to the arcane rules which your browser uses to decide when to repaint the page, to the byzantine rules for text segmentation and script-specific shaping engines used to let end-users interact with "plain text" content.
The question is whether this is necessary. I agree with you that people are doing all of those things. It's not, strictly speaking, necessary, it's just a popular choice.
