I think you can put it differently: Twitter has changed, the Guardian's target market remains the same. By by now there are so few educated middleclass people on Twitter that as a channel to that market, it's "simply not worth sinking more resources into" as the article says.
I’ve been thinking about this. X appears to be a far right extremist website exactly because extremist far left left en masse, leaving the square to far right people and people that don’t define themselves by what website they have an account on.
So yeah, counter-intuitive, but X appears right-y because leftists left.