You can make a slightly lighter, slightly stronger wheel, and depending on your priorities, it's a cheaper manufacturing process as well (hopefully to be passed on to the consumer), especially when we're talking about carbon fiber.
Bead hooks serve virtually no purpose for lower pressure tires. They're designed to bind clincher tires into the rim only when used with a tube. Without a tube, once you get above ~65-75PSI, a kevlar or wire bead will stretch over the rim and blow off because there's no tube binding the tire bead into the rim hook. That was the biggest hurdle in creating a tubeless road tire, and why the ultimate solution was a carbon bead with virtually no elasticity.
Since road tubeless hasn't really taken off and you wouldn't be able to use a standard clincher tire with a hookless road rim(1), you're unlikely to see a big push towards hookless road rims anytime soon. However, anyone interested in running a mountain bike tubeless setup isn't interested in running that sort of pressure so the stretching off the rim simply from being inflated becomes a non-issue. That combined with the reasons listed above are why you're seeing more and more mtb rims going with a hookless design.
(1)I've read that Alex has a prototype road rim in testing that's for tubeless and standard clinchers, but I just don't see how the latter would work.