Sometimes in team games you see newer players that build no units but tons of defense, and this is a strange thing: where could they have learned it? In other RTS games, low elos do weird stuff but zero unit pure tower is not one of them.
Well, mega porc is the meta in Co-op. This is the result of a number of factors:
1. Brutal AI is very aggressive, teams up in pushes and have few gaps of easily exploitable unit composition at lower force density: it will defeat normal player (not some top 20 micro-god) spread out to do map control while not having full econ due to teammates backline doing porc. Now a entire team pushing can do the job, but team coordination is never a given and porc always works.
2. Brutal AI generate a good density of defenses: raiding is not particularly effective when with fraction eco, especially when constrained to fairly poor micro. The raiding player runs out of units and can not mass for pushing normally.
3. Brutal AI is very stupid in dealing with defenses: it does not preserve units, avoid chokes, tech up properly with right composition, build arty/silo/shiny and instead feeds into heavy defenses (stringer/deso/cerb/luci) continuously. On a most simple level, brutal AI generate lance, Grizzly and phantom comps, but not building targeting impaler ball.
So, what does a new player to do after doing some of tutorials to learn to multiplayer? Join a co-op room! An inside he'd see co-op specialists players doing some chokepoint mega porc, building no units but constructors (or scorp, paladin to clean up after "impenetrable" porc is built). After failing other styles the new player would learn to porc hard to win at this, and may move into a normal team game and draw the ire of everyone else in the room.
Perhaps the AI should be changed to focus on anti-structure with things like sling and impaler, and actively try to counter terraform with constructor restore. This will make it weaker to players that fight it properly but will reward better habits as opposed to brittle cheese strategy.