By the same logic, other phonemakers can come over and make phones. The definition of what is a "market" is arbitrary and subjective. Google may be a monopoly in internet search, but only a small player in "global advertisement". And anyone anywhere is a monopolist in the very narrow definition of the market that includes their own ten customers.

What's really important is the power play: your company should strive to hold a comfortable and stable monopoly position in a meaningful market (meaningful to you), while the government's role is to watch over all the businesses so that large numbers of people are not under heavy influence of external forces and not made unhappy. If any product exploits its monopoly by shifting the power from the government or making people sad, then gov steps in and interprets the rules in the way to correct this. Or, the gov is corrupt and helps keep that monopoly going :-)