This is a fun, and I enjoyed the "CRT Dude" video because I resonate with that need to understand :-). One of the things I learned during that era was that there were a lot of computer makers but relatively few factories in China that were making things to assemble them. Because it was simpler to take the sheet metal work that was already designed and being made for brand 'x' and then differentiate on the case molding and electronics, a lot of the mechanical components were "re-used" (the factory can make 1000 or 10,000 with the tooling and the more they make the easier to amortize the tooling costs so the cheaper they can offer them).

I suspect when a company spec'd out a new design and then got all the tooling done, unless they explicit language in their contract about selling stuff made with the same tooling to others, the factories could pitch "we will do the basic case with no NRE[1]" and that was a bargain. As a result a lot of things ended up being "magically" similar in those days.

[1] NRE = Non-Recoverable Engineering which is the cost label for the engineering work to build the jigs and tooling that the factory will use to make the parts you want. Example an injected molded switch cover might cost $10,000 in NRE to make the molds that can produce 10 switch covers each and be used up to a 10,000 times. Then if you make 10,000 switch covers, you have used the mold one 1000 times and used up 10% of its lifetime. Cost of the plastic plus $1,000 (the 1/10th of the cost of the mold) are the real cost of those switch covers.