Because people are always willing to sell their ico coins less than what's on the market, the selling power will always be greater than the buying power unless in rear circumstances.
Less? you know nothing about that and you need more education. Less liquidity in the market create a big spread between the buy and sell order. When someone wanna sell his coin but there is not a lot of order in the market and that guy will create a big dump caused by the big gap on the buy order site doesn't enough to cover the amounts that will be dumped by the guy.