I have all the Yawning Portal adventures already from back in the day. Same with Saltmarsh.
What can I say - I'm fussy and I don't have endless time to sort the wheat the from the chaff. I find the great majority even of professional published RPG material to be mediocre at best. The stuff I have picked up on DM,s Guild doesn't inspire a lot of confidence.
When I'm paying for RPG content, I don't just expect top-notch ideas and writing. Layout and presentation mean a lot to me as well. Few creative types are also skilled at content presentation.
Call me old-fashioned, but I find value in commercial publishers hiring only the best house talent and freelancers, and supporting them with professional layout, editing, and artwork. There may be a handful of books on DM's Guild that suite my preferences, but at an unappealing cost in time and effort finding it, not to mention the dollar cost of printing it.
I just think WotC fails to support GMs well, and instead outsources that job to amateurs, third-party publishers, and Youtube channels. And presumably it's a business decision (keep costs as low as humanly possible), rather than a hobby-driven choice. Paizo has shown an RPG publisher can remain a viable business while releasing setting material and DM support at a much higher tempo.
I want to give WotC my money. Instead, even though I play 5E, I'm spending most of my DM budget on Pathfinder, 3.X, and even 4E adventure and setting material, and converting it to 5E.