It's not that simple. Imagine you build the next great thing, you open up a new product line for everyone. Your business starts doing well, but then Microsoft or Apple come along, throw money at it and include it in their bundles (Office or OS) by default.

Suddenly, you are the loser, while they are selling below investment cost to simply push you out of the market.

So that's the issue.

Similarly, it should probably be made illegal for VC-backed startups to undercut incumbents just to shut them down: that's very similar to me.