As long as you have free and open competition, then profit-maximizing companies will always out-grow companies that leave money on the table.

It's the same concept as natural selection. It'd be great if organisms didn't struggle all the time to maximize their reproductive fitness. But any organism that falls behind will be out-competed. Even if every current organism decides to "play fair", it won't be long until a hyper-competitive mutant takes advantage of the lull to destroy his counterparts.