I would say they are buying them from Amazon, not Ali Express. From what I've seen they've become less common as smart TVs have become more popular but people still buy them instead of Chromecasts, Fire TVs, and Nvidia Shields. It might have to do with them falling for the marketing claims of a 6K resolution and being great for gaming but a majority of the time it seems like they just need a burner device to add some kind of additional feature to their TV.

They'll plug in an external hard drive and watch movies, use them for emulation, or use it for Netflix because they have an older "dumb" TV.

I don't typically see people going through the effort of installing another OS. Maybe we are just in different circles.