The latter. As you say, finding panels that exist is easy even for a layman so it follows out of over 100 million monitors shipped per year at least one manufacturer would be using said all around vastly superior panel and you wouldn't have to DIY it.
I've used this method for repurposing laptop screens but I've never found it a significant cost saver (even ignoring time/labor) vs standard prebuilt monitors nor is anyone making such a panel exclusively for DYI-ers.
It's certainly true that for high-end displays I'd just go to Dell/LG/Samsung etc instead of AliExpress. Heck, anything that's premium enough to cover beyond sRGB is likely to be rare on Ali. But (imo) the biggest benefits of low price and easy accessibility to the low-mid end of products is the benefit.
Not saying that you can't get those 8k panels LG uses - but - sending 4k USD to someone over AliExpress feels quite risky even to me. You could probably get good stuff if you put in the effort but if you're earnings decent money from your CS job (I suppose most here are, I'm still a student) then it'll probably be easier to buy OEM/brand name.
I've used this method for repurposing laptop screens but I've never found it a significant cost saver (even ignoring time/labor) vs standard prebuilt monitors nor is anyone making such a panel exclusively for DYI-ers.