While cases like the scan-to-email trolls make the news, it's precisely because they are relatively rare. Tech media likes to hype these up and make it seem like there's a rash of these cases, studies by the GAO and a couple of scholars indicate that there is actually no patent troll crisis. While it's true that we have insufficient insight into the numbers for demand letters, there are very few other reported entities actually doing this. That said, I'd still like to see lot accountability and tracking of demand letters.
They aren't all that rare at all. But they also aren't typically as ridiculous as the print-to-scan patent trolling scheme.
Usually they go after medium sized fish and ask for ~100-200k. It's cheaper than a suit or an post grant review.
But even the medium fish are hundreds of millions / billion dollar companies.
The patent trolling going after the little guy is mostly exaggeration. Most trolls aim for deep pockets.
Plus you can lowball the shit out of trolls who send letters. Since you know they aren't serious. If they were, they'd never risk a declaratory judgement suit in a defendant favorable district. They'd just hit you in E.D. Tex or DE.