From John Grubar's Daring Fireball, who himself is quoting from The Verge:
Spotify isn’t just trying to become the biggest name in podcasting (which has heretofore been, but may no longer be, Apple). They’re trying to usurp podcasting as we know it — one of the last and brightest bastions of the open, simple, private, transparent internet — and turn it into a privately-owned, gated, complicated, invasive, utterly closed platform. Spotify is trying to do to podcasting what Facebook did to “having your own website”.
This is one of the reasons (Joe Rogan aside) that I left Spotify. Podcasting is a brightspot on the internet of how it was intended to be: open, private, and simple. Locking podcasts behind a Spotify subscription or tying it to sleezy levels of tracking means we're losing another piece of the original vision for the web.