In addition, everyone values a trade differently. It may appear lopsided, but given the circumstances e.g. roster depth, category needs etc, it may make sense to the manager that has accepted it. Also, you could 'win' a trade but it doesn't help your team, and you could 'lose' and it does help.
For these reasons it should only for trades that appear to be fishy that the veto comes into play. Not out of jealousy - which happens far too often.