My point was it's who is developing the software because it takes effort for another maintainer to step up and it doesn't always happen. Also if a commercial company digs a big enough moat with the open source product they could abuse it, so do you trust them now?
Similar to Google abusing Chromium, Castopod could one day be in that position if you don't support FOSS alternatives today. That would be the mindset to put yourself in.
That being said, I don't think it matters as much as the browser space, but I'm not in the podcast community. I could see though that it could potentially be very costly to have a monopoly for podcast hosting, but currently that's Spotify right?
Note: I have no preference here, just assuming what motivates GP's preference.