Because they are not street cops, they only have standard uniforms for police functions as dress uniforms. Tactical units are different from street cops. You are very much so concerned about them wearing camo when it means nothing. They could be wearing pink and it doesn't change a thing, what difference does it make that they are wearing camo? The individual officers do not choose what they get to wear, people are like "oh they think they are bad asses", but it wasn't their choice, individual departments have a budget and buy the gear they will wear. Have friends who are with the local SWAT, and they currently wear all tan/green mixed tactical gear, it's what the department issued them, and they can't buy their own uniform as they are supposed to look like a team and not a rag tag group with everyone wearing their own gear.
Tactical teams have been around since the 70's, maybe a google search on SWAT will help you?