To the original poster,
Wood stocks, in general, are fading away as the market has shifted, in part to reflect better synthetic stocks, in part because a fair amount of people got used to shooting using synthetic stocks from either the military or hunting rifles and now prefer them, and in part because of cost issues. Don't think that wood stocks will ever totally disappear due to aesthetic and emotional reasons but they probably will not represent the majority of the market either.
The primary militaries of the world has quit using wood stocks because for their uses, wood stocks are inferior to synthetic ones and the military does not care about looks.
Second, there is a large industrial base of manufacturers that are capable of making parts for the AR (which was actually part of the reason it was adopted after the M14 production fiasco) in the U.S. and other designs are proprietary to either manufacturers and/or national governments which creates a cost and manufacturing disadvantage to someone trying to offer an alternative in the U.S. The prices for alternatives reflect those issues.
A similar convergence in the market is the 10/22 which created a whole raft of cottage industries catering to it including buying aftermarket receivers and bolts. For a lot of .22 LR uses, the 10/22 is simply good enough and it is easier to adapt than some other designs to different uses.
Earlier in time, it was the Mauser (the 98 in particular) that had the advantage due to comparatively easy barrel and caliber changes and other features like controlled feed/good extraction, easy to clean, rugged, better safety, that made it a smash hit for hunting for a long time. For a time, there was a large amount of aftermarket triggers, iron sights, floorplates, safeties, etc. marketed for converting Mauser 98's and some of the commercial firearms at the time duplicated it as did the U.S. Military in its Springfield and M1917 rifles.
Regarding other issues, the U.S. military and manufacturers could design a firearm that lasted longer, used cutting edge materials, etc. But, one, it would take a lot of money and time to milspec those materials, might be much more difficult to machine and manufacture (machine tools and machinist time is a significant cost in manufacturing), probably cost significantly more, and probably only be marginally, if at all, more accurate and usable. As far as the ergonomics go, the AR is certainly not the worst on key operating controls such as the safety, etc. and its assembly and disassembly can be done in the field for a lot of the key components using minimal hand tools.
For the military, the AR is simply "good enough" and the adaptations to it over the years by the military have reflected changing needs and lessons learned from previous use. There is also the retraining issue that would exist if the military was to switch firearms. Contrary to the central importance of small arms to the firearms community, the military cares far more about other tools of killing and wounding which generally have caused the majority of casualties in recent conflicts dating from at least WWI and their spending in research and weapons procurement reflect this attitude.
BTW, I am not saying that the AR is the best design of all times for all purposes. I dislike the charging handle design and not crazy about the iron sights as formerly issued in the A2 series. I really dislike the twang from the spring and the military issue trigger pull. I find some of the small pins and springs difficult to deal with compared with other designs such as the AR hinge pins. The rifle appears cheap and fragile compared with the bulky battle rifles of yore (the Garand, the 1903 etc. ). But dog gone it, despite my dislike for it during my military service, even a homebuilt AR using relatively cheap components will shoot and shoot more accurately on average than most of my military bolt actions despite accurizing them. That feature alone brought me back to them.
Aesthetically, it is not the most pleasing to my eyes but then most of the current crop of military semi-autos are not. The bull pups, in particular, I find about as appealing as the STEN gun in appearance. Parts do break on it from time to time (the longrunning AR15.com dealing with Battlefield Vegas experiences gives a good highlight of these) and the need for new cartridges to adapt to the AR15 magazine well and receiver sizes has resulted in cartridges adapting to the rifle rather than building a rifle around the cartridge. The AR10 is actually more reflective of the 1950's as it represented full powered cartridges that were used by competitors such as the FAL or HK designs.
