Why would a team risk playing it ? If they lose the knife round its game over most of the time.
Teams veto nuke if they don't feel they have a very good T side, because it simply feels safer to not risk going down 14-1 or something like that and having to come back. Even if you start CT and you simply know your team isn't 100% solid on that side and you lose just 4 rounds you are already feeling pressured. Generally it is just a map most teams will only play if they feel very confident on it (or if they are just very bad on a lot of other maps) and that doesnt very often happen for both teams at the same time.
it doesnt matter whic side you are.
You are going to switch sides some point.
If other takes 15-0 on ct
You have equal chanses do same when you are on ct side to get 15-15
Having not played 1.6 nor CSS, how was nuke in the previous games, competive level?