If you can't profit off an enterprise, then there is not enough demand to justify your existance. If the market leader is going to undercut you to drive you out of business to then jack up prices to exploit consumers, assuming no artificial barriers to entering the market occur (mostly legal exploitation) or the price to entry is not too high, then as soon as they up their rates they reopen territory for competitors to arise.
In the end, if the market leader is constantly crushing competitors through undercutting to maintain their position, they are not really exploiting their customers at a monopoly and its a market win. It is still competition - the leader just moves to eliminate competition (which would piss off shareholders or anyone in general with a long term outlook on the company) rather than compete against it. As long as they cannot stop competition (and in a voluntary fair system, they cannot) then they have to deal with it one way or another.
In the end, if the market leader is constantly crushing competitors through undercutting to maintain their position, they are not really exploiting their customers at a monopoly and its a market win. It is still competition - the leader just moves to eliminate competition (which would piss off shareholders or anyone in general with a long term outlook on the company) rather than compete against it. As long as they cannot stop competition (and in a voluntary fair system, they cannot) then they have to deal with it one way or another.