This is why patents are "short". To offset the monopoly.
It's why you hear pharmaceutical companies whine patents are strong enough, they need them longer. Automobile makers, aeroplane makers, ship builders, and "industrial" companies that make machinery and equipment rarely complain, they are pretty much ok with their duration, they might like them a little shorter but could take it or leave it. And on the other end if the spectrum we have software companies who are forced into the game because of consumer electronics companies (for whom perhaps something between 5-10 years would be best) taking patents on "features" they wanted to make as software... And the software companies pretty much want 0-5 years because this stuff is a all mostly math, or irrelevant, or under better protection by copyright, etc.
Patent limits were devised as a one size fits all solution not taking any of this diversity into account.
