There are enough to create interest
The reason that they are popular is that once you have one in your hands and shoot it, you want one. The Army has never made a more handy light and powerful weapon.
The reason that they are $800-1200 is because part swappers are addicted to carbines and can't pass up anything that they perceive as rare. They may be dead wrong or taken to the cleaners by humpers, but they will still whip out that card and buy it. Part swappers are their own worst enemies, and when it reaches the point , which it has, that they find a pig in a poke and suspect it, but still say " I like it anyway", they deserve what they get. Because that pig in a poke will belong to some other poor sucker before too long, at $1200.
A mixmaster with a Rockola trigger housing will always go up
Part swappers can't help themselves. The fact that the carbine was updated to improve utility and durability escapes them. It is just a Rockola trigger housing surrounded by junk they don't need. That is why humpers are so successful, they even go to extraordinary steps like actually welding up evidence and refinishing them. They know that the swappers will still bite. When they discover that they've been duped, they don't care, the thrill of the chase is what they are after, not the carbine. A time will come when even a perfectly original carbine will not be worth more because the supply of these scarce guns has been so debased by swappers and restorers that the collecting public doesn't believe that ANYTHING is real. It is like that now as a portion of collectors who don't have an original piece or are not informed enough to really look, simply dismiss than any "Original" carbines exist. This justifies ruining as many guns as they want to make more "restorations" with humped up junk. It is a vicious circle and it will end badly for everyone who collects.
The only reason that carbines are part swapped is those letters on the parts
Restoring a carbine is just a matter of collecting all the right parts. The problem with the exercise is that 99% of the people wouldn't know the right parts if they walked up and stomped on their foot. What a small group of informed people did 25 years ago has no relation to the insane situation today. But it's entertainment.