At this stage, maybe a sophisticated player could, but not without first diverting resources away from their current intended purposes and considering the opportunity cost. Its not like those servers are just sitting around doing nothing. Any botnets are also competing always in flux with other botnets to do the same.
ASICs also have many flaws...
-ASICs can't match the ubiquity and accessibility of CPU mining which is more conducive to decentralization.
-Ostensibly harder to attack, but if successful, much harder to deploy new ASICs to fight back since they're in such short supply
-Large concentrated mining farms are easy to co-opt and regulate for governments.
-Heat, noise, and energy draw make ASIC mining obvious in general
-Everyone knows what you're doing with that ASIC miner
-Over half the hashpower now requires KYC
-No p2pool. Stratumv2 helps but isn't sufficient. Large pool operators control payout.
-Targeted censorship possible
I want to use the best tools for the job. Whatever carries the original spirit. I have no loyalty towards an individual coin or name just for it's own sake.