Earlier quoted context omitted.
Which works fine until they own a monopoly to a business with high cost of entry and decide to raise prices again. Things like this are rarely simple.
That's basically the fallacy of predatory pricing. It doesn't work. Sure, you can raise prices after killing the competition, but only so far as to not revive the competition. Your price ends up as the fair market price . Cost of entry is irrelevant here, it's a cost like any other.
If there is a constant threat of the prices being lowered again, it will be pointless to reinvest in restarting competition - the monopolist at any time can lower the prices back down.
Also, in some fields the monopolistic position gives network effects to the producer that cannot be replicated by an upstart, making a competition unlikely.