Carmack fulfilled his end by making a great engine, but gamers want more than these shooters have to offer. Given the dev budget they need to sell huge to recoup the losses, a decent game scoring 80% everywhere is not going to cut it. It would be a commercial flop like Rage.
Halflife2, Halo, Bioshock series, CoD4 (not Ghost), BF4, Team Fortress2, Portal(ignore this if u don't consider it a fps), and Farcry series raised the bar on what fps players want.
A generic shooter won't cut it especially with the need to recoup the ballooning dev budget. Crysis 2-3 with their mediocre sales were not flops because they had a smaller development budget.
ID has backed itself into a corner of needing to make an amazing game to recoup their 6 year development expenses.