The podcasts I listen to are available on all the major platforms
I think what we might be seeing is that the walled garden approach to content is not working out. People don't want to have to subscribe to a ton of services just to get access to a few pieces of unique content. There was a recent Disney+ thing to this effect recently too
I think the podcast market got ridiculously inflated when COVID hit, with every remotely known person starting a own podcast. Many more podcasts were created, so more of them also fade away now.
For the media industry it was fantastic. It was so damn cheap because everything was taken care of by the podcaster himself. They just had to observe if it can gain momentum on its own and then randomly decide to accelerate it with some additional ad-money or exclusivity contract.
This was shortly interrupted by a "let's acquire every media in the world / let's pay Joe Rogan 200 MILLION dollars for his podcast" hype, now it's back to "let's see which ones of chicklets will make it"...
Large podcast aggregators like Spotify have no real business model, they produce way to many shows with to fewer advertisers and subscribers to cover the cost and their audience isn't nearly as loyal those of TWIT.
Partly I believe that there's simply to many podcasts available, with to low content quality.
There are so many great podcasts that when gimlet shows went to Spotify, I missed them, but listened to other shows instead.
Spotify tried to acquire the biggest whales in the podcast market, thinking that it would be a revenue stream that wouldn't require paying massive royalties to record labels, which is why they've never made a profit on the music streaming side.
They overspent, buying up celebrity podcasts and creating some of their own, all financed with super-cheap capital that lasted until 2022 when interest rates rose globally. Interest in podcasts have also fallen since the stay-at-home peak, but Spotify added a layer of enshittification by splicing in ads into podcasts dynamically.
This is a massive UX fail because podcasts are supposed to be static audio files without additional monetization. But Spotify spent so much acquiring Rogan et al, they have no choice but to saturate podcasts with ads.
They never made a sustainable business by licensing music, and thus see podcasts as free real estate they can monetize without having to bay Universal, Warner, Atlantic etc.