If they paid indie artists properly, their operational budget would be much lower. Payola is the real reason why music doesn't play randomly almost anywhere anymore. It's even the case with many app music players that you download in app stores, the whole music industry is skewed to favor just a few well known and industry planted artists under the hood. And it's bent on getting worse..
If you hear an already popular TikTok song playing in the supermarket or at a gas station, it's literally driving royalties up for the involved artist. It's also why you rarely hear new music from small artists, and why Taylor Swift dominates news media every time she scratches her nose.
If you are regularly featured on the front page of YouTube, Spotify, and on CNN.Com, you dominate streaming now, and nobody else can get that spot without being backed by major money.
This is why I back up and always carry my own personal music collection. Streaming now is a generically engineered and controlled repetitive hellspot for me without real choice.
Spotify will only repeat a song during shuffle if you also activate repeat. It will also repeat a song if you actually added the song twice or more to said playlist. You can try it out by shuffling a playlist+deactivate repeat then check which songs have been queued from start to finish.
Smart Shuffle -despite the name- is more a playlist function than a shuffle function. It's like the Radio playlists but with the songs interspersed temporarily in your own playlist. Note that these songs were not already in your playlist - so they do not repeat unless you activate repeat.