In your imagined world only the rich investors or companies have money and all the risks have to be large sums. I think the idea of a maximum margin is to limit the hoarding of profits thus requiring cooperation and smaller but more numerous investments. Micro/crowd investing could raise large sums of capital for larger projects that many people want to take a (small) risk on. I.E. enough businesses/people want better fabs (including a consortium of smaller chip designers that would share them) so they pool the risk and money and make it happen. It requires vastly more communication and cooperation, and thus likely wasn't practical before the net.
I don't know that margin caps are the best option, but certainly that is the end result of competition (a preferable more responsive and free system that is prone to corruption). I would be interested in testing something like the maximum size of your company is inversely proportional to your legal margin cap. Small businesses could have high margins and behemoths would be greatly restricted.