I understand that's Kite's perspective (and yours -- "purchasing won't pay for this"), but devs are
not paid meager salaries in general, and definitely might care about their code quality when it's put out in 'public' whether that be internal repos, or github.
Payscale estimates average engineering salary as having between $3,000 and $7,000 a month more in disposable income over writers -- and I would guess almost every professional writer pays for grammarly.
But, I agree that this is a new concept, and just spitballing -- right now, these sorts of linters and code formatting tools are mostly open source, so it would be some product marketing work to see if the market would actually pay.