The benefit of patents is that you have to make your patent public. After the patent runs out anybody can reproduce what you patented exactly like your did.
The problem, of course, is that many companies see patents as a way to rent-seek. Establish enough patents in your niche and now nobody can compete with you. This is particularly a problem in the modern world where technological advancements have accelerated so much that a 20 year long patent is an eternity. An entire industry can just die off in that time.
That's the idea behind it. The reality is that patents are written in a way to reveal as few as possible while blocking other companies as much as possible.
The problem, of course, is that many companies see patents as a way to rent-seek. Establish enough patents in your niche and now nobody can compete with you. This is particularly a problem in the modern world where technological advancements have accelerated so much that a 20 year long patent is an eternity. An entire industry can just die off in that time.