We have to differentiate between actual prevent defenses, which involve dropping everyone into deep zones, vs only rushing 3 guys and still playing a more aggressive coverage. A 3 man rush can be situationally effective and you see it more and more. A 4 man rush is by far the most popular by any team at any level but it's a natural compromise because there are 8 defensive zones to cover by only 7 players.
The key is to rush 3 but not make it look like you're rushing 3. Often times in a 4 man rush, your inside guys are mostly applying enough pressure to let your outside guys get 1 on 1 match ups. What if you make it look like you're rushing 5 or 6, get the interior guys blocking ghosts, but really only rush 3 and still get those juicy outside pass rush matchups while dropping 8 into coverage? Pressure isn't always about getting there, but just making them think you can get there and throwing short.
This kind of thing is why you're seeing so many hybrid defenses. Offenses want to be bean counters, so defenses are spilling the beans.