Even before Dangit Grandpa, you had Laissez’s Faire to blame for a lot of the decay. LF was a political subforum that degenerated into leftist hackery and was mostly unmoderated, though it became so bad that Lowtax moved it into a special subforum called exceptional Forum for Assholes with a hideous stylesheet and heavy penalties that got applied to your account just for posting there.
It continued to degenerate, though, until Lowtax literally got a Secret Service visit because posters were talking about murdering President Obama for not being woke enough. Not long after that, Laissez’s Faire was shut down entirely, and the goons once quarantined there proceeded to impose themselves on the rest of the forums.
I would argue that that doesn't really matter - if SA remained a fun place to be, fun people would be there - regarldess of other forum's drama. It survived so many more (and larger) issues, such as the mod staff covering for a pedophile and a diaper furry being a main-site contirubtor.
SA was already dying by the time of Dangit Grampa, or LF, or really anything - if SA was "alive" they would have been able to survive those things easily, like they had in the past, by having "real" posters mock them relentlessly. However, most of the "real" posters fucked off to wherever else at that point so it was just a roving band of lunatics moving into a deserted town.
Lowtax literally did nothing as people left his forums/website, some very prominent people among them, and missed
several huge opportunities along the way, because of apathy.
It's really worth pointing out that everything Lowtax, himself, did was really shitty and half assed - which was
primairly shipping/processing shit from the Something Awful store. It was always a problem, there were
always delays and stories about why product was late instead of it running like an actual store was expected to. This meant, of course, that it never grew into anything - because Lowtax half-assed it. There were
countless projects that grew out of SomethingAwful that Lowtax took 0 advantage of and makes 0 revenue off of, as a result - huge piles of money just left on the table because he'd rather do nothing.