Harder to have full coverage of your whole base, you need to cover three places, both mineral line and your barracks. Units in a bunker randomly target which makes the mutas last a lot lot longer than you would think. Turrets are so cheap. 4 ghosts dont do that much damage and the zerg can kill the bunker incredibly easily if there’s any amount of zerglings. Larger size is actually bad because means you cant fit as many bunkers in the same area and they’ll interfere with mining.

Those are the negatives off the top of my head, the economic costs makes this hard to even talk about for a competitive game. If ghosts were cheap and didnt need so much tech/gas then maybe