@doubleome Because DICE wants to promote co-op play without actually having systems in the game to promote co-op play, hoping folks will just do it organically.
Rao CAN be insanely strong with a coordinated group in terms of eliminating vehicles, and even solo can be effective at "area denial" for vehicles if he can find a remotely safe place to hack from. But to your point...playing "area denial" on Rao is like watching paint dry. It's boring and lame, even if you're running the M5/Stinger to try to combo vehicles, or C5 to try to blow up ground vehicles you can get close to (hoping that the passengers all stop thinking and nobody exits the hacked vehicle to simply shoot you).
This is a problem for many of the specialists. Some like Mackay, Falk, Sundance, or even Dozer have "generally useful" kits that work in a wide range of situations. Others like Rao, and as the devs pointed out Irish, have far more "niche" roles for their toolkits - driven in part by challenge completion (seriously, needing to destroy grenades to progress Irish feels like trash compared to how "easy" other characters progression tracks are like healing people as Falck).
Honestly I think the whole vehicle design at its core, both ground and especially air, is fundamentally flawed and that we're never going to get a "good feeling" game that has any semblance of balance between that design and how specialists operate.
If people aren't picking a specialists, it's not because they don't know how to use the specialist in all instances as the devs implied on their 1.2 video. It's because many of those specialists are too niche, and in a game where the majority of the design is focused on supporting solo-play these characters that are inherently co-op oriented and whose kits don't lend to solo play will see less playtime in general.
DICE has always struggled with balance, and I'm still mystified why they thought that taking the already tricky balance they struggled to maintain and adding an Everest-size mountain of complexity with specialists was a good idea. Sure the concept is nice and all, but it should have been clear very early that the direction was not going to lend itself to an overall positive experience, and would instead just eat up a massive amount of additional development time towards frequently tweaking, balancing, updating, and changing specialist kits that aren't performing in-line with expectations.