Why Map Pick always Attackers

Why does the team that gets to pick the Map always start attackers? Is it because most maps are Defense favored so they are trying to even out for the fact that one team picks more maps than the other in a Bo3/Bo5?

if team A picks the map then team B picks def or att side

we have a lot of Knife Skins but no Knife Round as a decider haha

Why I powder my cradle and not the baby.