I have two additional theories for why the boomers are more prone to spreading fake news.
Maturity
Every person, demographic adopting a new media has to go through the whole maturity cycle anew. We've all been there. (For me it was CompuServe, BIX, FidoNet.) We've always had trolls, memes, jokes etc. So netiquette and its predecessors emerge. It takes a while for the novelty to wear off, cooler heads to prevail.
Entertainment Becomes Reality
Boomers are bored. One article I read quoted a few boomer trolls who regarded fake news as funny, a way to pass the time. No different than the supermarket tabloids.
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Alas.
Like when the AOL noob tsunami flooded the web, obliterating the indigenous culture, there's a huge cohort of boomers adopting Facebook. Fed and supported by boomerbots, of course, they're having an outsized impact.
More sadly, I fear most boomers are no longer teachable, more so as they age. So they're not likely to adapt or develop their own netiquette. I've all but stopped talking politics with my older relatives. Because they have no memory of prior discussions. Just like Groundhog Day.
Lastly, how we talk changes how we think. Propaganda works. This is more than confirmation bias feedback loops (mentioned elsewhere). This is something like brainwashing. My mom's boyfriend got her watching Fox News and cable news. She's transmuted from educated, progressive, liberated powerful woman (earned a masters degree, marched in DC to support abortion rights) to almost complete dittohead. This "captured by a cult" story is sadly common.
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The only remedy I can think of is turn off their TVs, log them off facebook. Keep them distracted with knitting, puppies, and church.
My elders are now basically shut ins. Plugged into the TV. They'll happily watch happy shows, like Antique Roadshow, nature shows, cooking.
But when the nontoxic programming ends, they go back to the default channels of Fox News, CNN, and manufactured outrage.
I tried to figure out how to reprogram their TVs, cable boxes to exclude the toxic stuff.
But what's needed is an eldercare streaming TV apps. Like parental controls, but for our parents instead of our kids.