Thinking about it, the real problem is that the market is finite in size. In an infinite market, being a monopoly is impossible (although anticompetitive behaviour should still be discouraged). The problem comes when one fish gets too big for the pond.
I can't really imagine an "infinite" market. The biggest one I can imagine is an ultra-global one, where every living human anywhere can buy anything from anywhere and get it reasonably quickly. In such a market, monopolies would be global monopolies.
Actually, come to think of it, the market for digital services is quite "ultra-global" already.
Either way, whatever the market size is, monopolies in a given market is the the victory condition - the goal - for the monopolist, and a failure mode for the entire market. Hence how it works is that the idea of "the win" is dangled in front of you so that you work, but it's meant to be snatched away in the last moment, so that you never reach it.
