I think as computers have advanced in power the technology that runs on them increases in complexity to utilize the new power. With economies that prioritize growth, people in charge of things like web standards want new ways to innovate over their competitors. Developers don't want the power afforded by additional computing cycles to go to waste. They also find things lacking, like the difficulty of accomplishing "holy-grail" webpage layouts. Standards are expanded to accommodate these pain points, and new features are added, but nothing can be taken away as this would break things that already work. This continues to the point where the web implodes under a plethora of animated SVG hammers striking anvils and autoplaying videos.
Thinking of it another way, computers of a long time ago could do only basic things like printing strings or drawing lines. Computers of today can still do those things, in addition to a host of other things that are now only possible due to technological advancement, like streaming video. But in some environments it is possible to limit yourself to having the computer do just the simple things - it's just a matter of deliberately opting-in rather than doing the only thing that's possible to do. For example I'm trying to write a "Web 1.0" webpage in the style of early 2000's design like Praystation[1], ignoring the shiny new technologies that do a lot more, because I believe that "more" is not necessarily "better". I believe you have to be ideologically motivated to do this now, because it seems like a lot of average web users have come to expect SPA-style apps with fancy animations and client-side interactivity, and that's where a lot of interest in web design appears to lie at present.
Of course, for a video-sharing app this doesn't really apply because the platform it runs on was proliferated fairly recently. The oldest model in the smartphone lineage came out at the start of 2007, and in order to build apps for it, it was necessary to install a full-blown developer toolchain with visual layouting tools and hundreds of APIs available for use. That's the simplest it can get. In the 1980's you could just 20 PRINT "HELLO WORLD".
I think it would greatly help if the author published the source code, as he briefly mentions considering. At least then it would be possible to judge exactly how technically complex the software is, and people could learn from it also.
However, at the point where you need to rely on complex cloud infrastructure like AWS to build things like video sharing applications, it might turn off anyone not completely interested/invested in app building. Although, I do believe a completely invested/motivated 16-year-old could pull off something similar, given the amount of documentation and free libraries on the web. That's not discounting the difficulty of actually accomplishing such a thing - for a young newcomer it would be necessary to learn many disjoint concepts for such a thing as video streaming. But given a significant amount of effort and motivation, it's at least possible to do in the present age.
[1] https://joshuadavis.com/ps2-praystation-v4