The alleged economic incentive suggested in the article, that Google wants to deal with "established big players" is literally nonsensical, something that the article itself arrives at, weirdly enough.
"But we later realized the shadowban really was about the type of website we are (i.e., small and independent). While Google gives large publishers an appeal and recovery process, small and independent publishers have no path to appeal our shadowbans.[...]"
That's not an indication of Google liking big players, it's the opposite. Big players have leverage against Google, you the small publisher do not, as you correctly identified in the case of reddit:
"[...]Unlike independent publishers, though, Reddit actually had leverage over Google. Reddit was the owner of a trove of historical user generated content that Google wanted for its grand AI plans. If Google could secure a deal for Reddit’s content, maybe that would spare Google the expense of negotiating licensing deals with the web’s many disparate publishers and rightsholders."
Google doesn't need to negotiate with you, they can kill independent publishers, which is why you're writing this blogpost. That's the entire logic of the internet platform economy. Kill traditional distributors, abuse atomized content creators. Youtube and Google hate publishers as much as Uber hates taxi companies and unions.
Which is why the literal reason given by Google is much more likely, they just don't think your content is good.