tl;dr: CAS too expensive so in some games no players spawn, causing first-spawn SPAA players to get bored and not play SPAA anymore
When CAS was more easily accessible, a lot of less-skilled players were able to spawn aircraft more consistently. While on the surface this may seem like a bad thing, this gave first-spawn SPAA players guaranteed gameplay.
The current issue with CAS (exclusing LDIRCM helicopters) is that for the majority of time, SPAA systems are only spawned AFTER a CAS aircraft has made its attack run. This is due to SPAA gameplay being exceedingly boring as in many BRs, you will often see nothing more than a couple scout drones per game.
This is in addition to most low-skilled players being essentially locked out of CAS so there’s less easy kills if you’re playing SPAA.
While you may not notice, you will often be saved from CAS by a friendly SPAA that first spawned (if they didn’t die to an enemy tank) almost every game there’s one in your team, until they get overwhelmed or die to a better player which would already have gotten enough SP for CAS even if it was more expensive.
Small rant
PLEASE SPAWN MORE JETS I HAVE NOTHING TO KILL AT 9.3-11.0, I JUST HAVE TO BEG FOR RUSSIAN TEAMS TO SPAWN SU-25S TO GET ANY KILL