A patent grants the right to exclude others from making/using/selling an invention; it does NOT grant the patent holder the actual right to make/use/sell the invention. And the actual scope of most patents is much narrower than you might think. In the vast, vast majority of cases, a patent does not guarantee any sort of dominance in the market (as might be implied by the word "monopoly").

Most patents are for inventions that merely represent incremental improvements over existing technology. The existing technology itself may be covered by a host of other patents owned by others. It is hardly ever one patent that covers an entire product. Each relevant patent is simply a bargaining chip that may give the holder some power in the marketplace but not what one would think of as monopolizing power.