Why?
There are only 5 maps in the pool right now (even less historically) so why do teams have an instaban? It should be expected that they know how to play 5 maps well, and change their veto depending on their opponent. Maybe when there is 6 or 7 maps like in CS but right now teams have no excuse to ignore 1 map.
P.S. why is it always Split? I love Split :(