People tend to overestimate how reasonable it is to become a real competitor. Just because someone's sitting on a fluffy market with fat margins doesn't mean competition will just fly in and regulate pricing structures down for consumers.

Typically, quite the opposite happens and investors and entrepreneurs see the opportunity to compete, but quickly discount it because the risk to compete is too high relative to barriers to entry. As long as your barriers to entry are high enough, a bonus if on of the barriers is capital intensive (time is something many can sacrifice but capital can be conjured out of thin air), you're going to be nearly impossible to dethrone by a competitor coming in.

You can usually spot competitors a mile away approaching the outermost mote your castle has and head them off early, perhaps establish an early friendship, or acquire them at a low cost before they get anywhere near the crown jewels. The trick is to get the foothold and momentum in a market. After that it's difficult for competitors to actually compete unless you're asleep at the wheel.