It's obvious that patent holders/trolls wait until their infringed-upon patent becomes profitable before they decide to sue the companies that made it profitable. Why is this allowed to happen? Shouldn't the patent holder be responsible for defending their patent as soon as they know that it is being violated? It seems we would have less problems with patent-trolling if the prize at the end of lawsuit wasn't so big.
<i>Why is this allowed to happen?</i><p>IANAL, but in general if you can show that a patent holder deliberately delayed enforcing their patent, any award of damages will be reduced under the clean hands doctrine.<p>That said, there are many cases where patent enforcement takes a long time for no fault of the patent holder. If the patent holder is an individual who doesn't have big pockets, it might take a few years before he is aware that his patent is being infringed; he might spend a year trying to get the infringing company to negotiate a licensing deal; he might spend a year trying to find a law firm willing to take the case on contingency; and that law firm might spend a year trying to negotiate and/or collecting evidence before actually launching a lawsuit. So even without any deliberate attempts to delay enforcement it's entirely possible for a patent to be infringed for five years or more before a lawsuit happens.