Say what you will about the trolls; these guys have it figured out. They're targeting people with enough cash to make it go away, but not enough to mount a proper defence. Prior art doesn't enter the picture, as the trolls' targets are unlikely to retain counsel. When it costs as much to retain a lawyer as it does to make the issue go away, it's perfectly rational for the small business owner to pay up and move on. Tragedy of the commons at its finest. It's cynical, reprehensible, and evil, but it's a pretty solid business model.

An acquaintance of mine goes by bars, small stores and coffee shops in his town. He tells them that he knows the neighbourhood pretty well, and that for the low, low fee of $400 a month, he can make sure that their store doesn't burn down or get trashed. It's cynical, reprehensible, and evil, but it's a pretty solid business model.

Nobody's saying it isn't a protection racket, just that it makes more sense for individual business owners to pay the extortion than to tangle with the mob, even if the net result is everyone having to pay extortion to a powerful mafia.

Is it just bluffing?

The existence of packet radio doesn't necessarily constitute prior art. The patents are far more likely to be on certain very narrowly defined processes that are arguably implemented in a WiFi system than on a very broad field like "digital communication over radio". If the hams didn't use the particular techniques at issue, then that wouldn't constitute prior art.

You really need to read the specific claims in the patents themselves to figure out how to invalidate or avoid the patents.