This is a very good question I am glad someone brought it up. Is it weird to anyone else why in close to 100yrs why a carbine bolt action hasn't been made for certain said troops here? I know the Jungle Enfields were real popular and overseas many bullpup designs have taken off well with certain Mil. and Police but over here, it's kinda over looked huh
-Aaron
Carbines are still issued to US troops, just not in a bolt-action variety. The US issues the M-4 Carbine, which is basically a 14.5" M-16 with a telescoping stock. I know, that's oversimplified, but it makes the point.
As for bullpups, most of them have a limitation I, personally, find unacceptable. Most bullpups either cannot be used left-handed, or require a conversion which makes them unable to be used right-handed. While this may not be a big deal for most, 1 in every 6 shooters, myself included is left-handed. If you convert to left-handed use, a right-handed person can't, in an emergency, pick up the bullpup and use it. In the military, this could be very devastating.
FN has come up with a solution to this in their P-90 and FS2000 bullpups, and hopefully that will catch on.