A monopoly can end, it is not perpetual.

Sure in your example as a single user you don't have the power to enforce or prolong your monopoly and many companies are the same. They can use their position and maintain it, but they often cannot prevent others taking a foothold. What often holds others back is that the more a market is dominate by a single force; the more money you have to put into the pot early on and for a longer period to break that hold.

Look at how Epic is spending a fortune to break Steam's near monopoly on the computer game market for PC software sales. Look at how Sony threw insane money into sensor development in order to steal a significant slice of the photography market from the joint giants of Nikon and Canon.



Monopolies do fall - indeed historically speaking they have ALL fallen. Even giants like Google and Microsoft can and, one day, likely will fall to a competitor.