Prusa's machines are expensive but by and large "just work", and keep on working, and have a strong reputation for this, backed by them eating their own dogfood, producing printers with their printers.
The clones are almost always require a lot of tweaking/fixes/upgrades and aren't durable or reliable. Some of them are downright dangerous in terms of being fire hazards, with things like heater bed wires that fray and short out, underspec'd electronics that overheat, shitty firmware, etc.
He's got a thousand (mostly) Chinese copycatters who immediately download the design, figure out how to squeeze every penny out of the BOM, modify it slightly to give their marketing people something to brag about being "better" (as well as try and force people to go to them, and only them, for replacement parts), and print money from tens of thousands of people on reddit and Facebook 3d printing forums who think they're scoring some sort of great deal. None of these people are adding anything of value; in fact, all the effort spent fixing the shitty clones that are very poorly supported, probably results in millions of person-hours wasted.
If I were Prusa, I'd be exhausted, too. It's not an understatement to say that he has been not-quite-single-handedly carrying the hardware side of the enthusiast/cottage-industry FDM market for well over a decade. Sure, you have the corexy and delta designs, but they're definitely a minority.