Just different sources. Take your pick.
Generally TuneIn has streams of live radio stations and podcasts.
Streaming (old Slacker) plays song “types” on demand in an infinitely skippable radio format without ads.
Spotify came after both those because Tesla did not have the rights to use Slacker in the EU. EU cars did not have slacker and only Spotify so they are similar. In the US, Spotify needs a premium account to get any usefulness from it. Spotify recently added podcasts but were not available in the Tesla Spotify app. I’ve heard the newest software adds support for these.
Best thing to do is to explore both and see what fits your listening style best.