Speds and lolcows are different. For me, events that have been the biggest lolcow factories have been the battles between nerds and SJWs - Gamergate, Comicsgate, Weeb Wars, all have produced numerous cows on both sides.
Tumblr is a haven for them, and certainly encourages lolcalves into lolcowdom, but it also is a lot of stupid teenagers that will grow out of it. Troon activists are almost all lolcows, as the Rat King amply demonstrates, but that's because troons are lolcows, and the activists (well, 'activists') are the loudest of them. Twitter doesn't so much produce lolcows as allow them to thrive and spread their toxicity.
I'd say the best incubators or factories, though, are hugbox forums like ResetEra, PULL, Metafilter, Something Awful, certain subreddits and fan forums where the extermination of wrongthink leads to an expotential explosion of exceptionalism. They're inevitably focussed on the extreme sides of the political spectrum (though the ones I've listed are all heavily identitarian), they steadily shed their normal members, and they end up with concentrated autists who simultaneously think they're the part of the best forum there is that is also completely corrupted by whatever groups they regard as their nemeses.
The most prominent users and moderators of these places either start as lolcows, or become so as the hugbox tightens and they don't escape because they need to keep up. They also inevitably advocate more and more violence over whatever angers them, from politics to a computer game to the colour of a Pokemon, while staying safely hidden behind their keyboard. It's how you get death threats over headcanons and discussion of bombing entire states for safety.