The military does use parafoils for quite a few of the special ops organizations. They're really not well suited to a mass airdrop. First, those parafoils are a lot more expensive than a simple round chute. Second, the parafoils require more skill to fly than a regular chute. I once saw a female skydiver who had to make a downwind landing because someone cut her off. She hit the ground with a forward speed of about 25 MPH and didn't get up for quite a while. Now, imagine the situation with hundreds of jumpers going into the same DZ. Chaos would be putting it mildly. Finally, most paratrooper jumps are at low altitude. My jumps were all at 1200 feet except for a couple helicopter jumps from 1500. 1200 feet is only about 11 seconds from the ground. It takes about 4 seconds for a main chute (at least the ones I used) to open, so if you have a major malfunction you're only about 7 seconds from the ground. A parafoil chute isn't quite as reliable as a round one and when it fails, it often spins the jumper to a pretty high RPM rate requiring a cut-away of the failed chute before you attempt to open the reserve. That doesn't give you a lot of time before you hit the ground. A combat jump is much lower, sometimes even before 500 feet. On those, they sometimes don't even bother carrying a reserve chute because you'd never have a chance to open it. Reliability is an important thing...

The special ops forces that use parafoils are small teams that frequently jump in from very high altitude. A HALO (high altitude, low opening) jump might be from a C-130 flying at 25,000 feet or higher. The plane never slows down so there's little chance that anyone on the ground would know janyone had jumped. The team might wait until they're below 2000 feet high before opening their chute. Depending on the mission, they may then drop into water and have to swim a few miles to shore. Those are some pretty studly dudes.

About the malfunction rate, that brought back some memories. When I went through jump school in 1975, we were still using the old T-10 parachute for most of our jumps. My class was the first to get to use the MC1-1B maneuverable canopy at jump school. It had several nice features, including a limited maneuverability, a nicer harness instead of the old "nut cracker" model, and an anti-inversion net. That's a small net that extends down the suspension lines for a couple feet and really reduces the chances of an inversion (where the canopy deploys through the suspension lines, the most common type is the partial inversion where the canopy looks like an enormous bra. This is called a Mae West.) Anyway, we made 4 jumps with the old T-10, and it used to have a fairly high inversion rate, especially with rookie jumpers who didn't hit a good body position when leaving the plane. At Benning, they had big loudspeakers along the drop zone. When someone had a problem, the instructors would call out, "Jumper with the malfunction, activate your reserve." It seemed just about every pass (20-30 jumpers) had a malfunction, and every time the loud speaker announcement was made, at least two or three guys would pull their reserve. Man, did they catch crap when they hit the ground!

As bad as it was at Benning, it was worse at Fort Bragg. Their main drop zone was nicknamed "Malfunction Junction." Of course, a lot of that was due to the way they jumped. They'd clear a plane very quickly, so they sometimes interfered with each other's chute opening.