Machine muscle was an argument people tended to use years ago when more than 1v1 was a thing & ran like crap on older hardware, and yeah, it was a legitimate reason for it to not happen at the time.
However the real reason it vanished was far simpler - It was shit.
For people who keep demanding 2v2 etc and never read what we keep repeating:
3 & 4 player TB did exist, was tested, and was scrapped because it sucked. Simple as that. It remained as a single player thing for a while, then was eventually removed from the game completely.
If people want hampa's official views on it then go dig for the interview he did with LesDuncan on Twitch years ago, it inevitably came up as a question and got a longer version of the above as an answer.