Beyond being a direct competitor to aspects of the NYT’s business, their platform and pro-free-speech ethos are an existential threat to the corporate media (like NYT) monopoly on the Overton window.
But yes, there’s clearly a resentment from within elite media (WaPo/NYTimes) that people they don’t like have an avenue for editorial independence that is beyond their reach.
From the horse's mouth- https://www.nytimes.com/2021/04/11/business/media/substack-n...
I didn't know about Substack before, but now I do! :D