This presumes that most orders are already in the market and that most people don't use market orders which is not the case. As for why 90% lose, well a while back we had a member who was high up in a SB company explain that as a SB broker they really didn't need to manipulate anything as the behavior of their clients made it easy for them.
What most people did was to not close losing orders quickly enough so running up larger losses than they should have allowed coupled with taking a small amount of profit too quickly.
When you consider that all markets do not go straight up or down and that there may be retraces to entry points quite often, this hits people on a psychological level so holding a winning trade that eventually makes a good profit is not easy to do. The same applies to a losing trade that moves closer to breakeven a few times then goes back into more loss which people will tend to hold on to.
It really is very easy to see why most people lose when you consider the above behavior patterns in my view.