This was changed exclusively for 3v3 and 4v4 because howitzers were OP in the big team games according to the balance team
Not overpowered, but completely cancer to play against. Players could easily get away with building at least 3 of them (while teammates hold the line) and randomly barraging the entire map constantly, getting random wipes left and right. And getting a bunch of random players to coordinate doctrinal bombing strikes is genuinely often next to impossible, unless you happen to get matched with some rank <100 players that communicate and speak English (very rare). I personally find that the quality of the average 3v3 and 4v4 has massively improved since then, though it's unfortunate (1v1s and) 2v2s had to suffer because of it. I think a small popcap decrease should be fine to make them a bit more accessible across all modes.