Revenue share isn't the only issue developers and publishers have with modern Steam. There's issues with (lack of) curation, bloat of titles, indirect vs direct marketing, their content/user algorithms, user reviews, etc. Revenue share is just the most direct monetary reason, but it's not the only reason, and that's why you see developers shucking Steam but maintaining releases for Xbox, PS, Nintendo, and sometimes even other PC distribution platforms.
A lot of the things that Steam enthusiasts love about Steam - they don't curate their storefront methodically (the curation argument again), they don't directly advertise specific titles (it's mostly algorithmic), they don't directly push product on customers (it's mostly algorithmic), because the previous three - there's a huge selection of titles making competition, especially for indies, much harder than smaller storefronts like Switch or even PS/Xbox (the mobile games store issue), and putting more not just control but responsibility into the hands of the user.
Those are all negatives to publishers when other stores offer better solutions - for publishers - that users may personally like less. It's easy to see why you'd want to sell your thing on a store that has a level of exclusivity - giving the appearance of 'premier' product quality, that has less competition, better advertising opportunities, that doesn't have the chance of pushing your product next to shovel-ware, malware, porn, etc., and - on top of that - has a better revenue split on the same platform.
As a publisher, it's a no-brainer. It doesn't mean you'll like it or that it's better for customers, but it's not hard to see why developers are all doing the same thing. It's not just a moneyhat issue. Steam has problems outside of the revenue share.