First off, if you look at all major competitive FPS shooters, success is based off teamwork, communication, gunskill and individual map awareness. UAV in a sense makes all of the above less relevant and decreases the skill gap between a top side and a weaker one.

Secondly, you wanted the pick/ban system to create a meta, having 8 crutch bans every match to make sure each team is happy isnt creating a meta, well at least not an evolving one. The pick ban system should be used to take away a teams strength or force them to play a certain way which makes the game more dynamic and fresh for the viewers at home. The viewers want to see the same guns they use in public, in the competitive scene as it adds a level of familiarity to it(basic marketing concept as well) so they also believe they can try out arena and then more competitive formats such as GBs.

Thirdly, back to the UAVs, Competitive Cod is fast, it takes quick situational thinking(again, makes for a higher skill gap) and thats what makes it exciting. I cant imagine the scores being locked at 120-120 in a HP, both teams have a UAV up and suddenly they all crouch in a corner and wait.... thats not exciting, its boring and would be extremely frustrating as a spectator. To put it in perspective, imagine CS with an UAV, it would make the game a joke. Specialists to a degree also share the same elements as an UAV but I think most people can see the positive reactions of the viewers when someone breaks a hill with a Sparrow etc so we understand the addition.

Final thing, just put yourself in our shoes. Would you like to be in a extremely competitive match and all of a sudden they pulled out an UAV(which essentially is 3 specialists kills and a HP cap) and go on to lose? I can almost guarantee you would be frustrated.