Troy is correct. Actually building the rifle isn't the problem...parts availability is. Just by knowing what they build, I count 16 different basic barrels, 4 uppers, 15 handguards, 12 stocks, etc..If their manufacturer/vendor relationship is like every other with which I am familiar in the firearms industry, they're ordering barrels 2+ months ahead, and trying to estimate both supply and demand so as to not run out before the new ones get in. Also, its not as easy as it would seem to just call a vendor and say "hey, we're short 5000 extractors...can you red label them to me?" The parts houses do runs based on anticipated demand...if they run out before the next scheduled run, anyone buying from them waits as well.
Another factor is when the dealer actually orders the rifle. While some do it right away, others don't. Some only order one day each week. Some wait to see if they can combine orders to save on shipping. Others "get around to it when they can". We all like to think its the other guy's dealer, but sometimes it's our FFL guy as well. Since they "build to order", if there's no order, there's no build.
Old Tiger is also partially correct. Two-stage triggers can take 15 minutes each...but generally only about 5-10. But even at that rate, cranking out hundreds of triggers takes time. That they include it as a standard feature rather than as an expensive upgrade says a lot them.
Gotta go.
Sluggo