

It may have a large part to do with where in the UK you were coming from, and where in the US you wound up, in fairness. Bog-standard eggs are $8/dozen just outside a major metro on the East Coast, while less than half that for posters in other regions. Last week, I was in Manchester, and a 15-pack of eggs at the Lidl on Piccadily Gardens was about £3 or so, which would probably make $8/dozen seem pretty crazy in comparison. I think the lowest I saw while there, further from the city center, was £2.15 for 15 eggs.
I don’t think it was sheer numbers of users that made 3rd party apps a big deal, but who was using them. Someone would need to actually do some research to confirm or refute it, but my experience was that they were disproportionately favored by power users, i.e. the really prolific posters and commenters that you would come to know and recognize after spending a bit of time in certain subs. If enough of those people decided they couldn’t be convinced to use the mobile site or official app, you’d probably have some small amount of previous lurkers step up their posting a bit, and bots.
From what everyone says when they mention the current state of the site, it mostly sounds like it’s bots just spamming reposts and arguing with each other with recycled comments originally posted by other users.