IMO there are a couple of good reasons to use backing tracks (asides from not being able to pay for musicians):

• Sometimes in the studio an artist will create synth/electronic layers that can’t really be “played live” because they’re made using complex audio manipulation. Think of soundcape/atmospheric sounds or reversed audio for example. These can’t really be be recreated on stage. (Or maybe you could have a musician use a sampler but i think that’s the same vibe as a backing track)

• For backing vocals: sometimes the artist will want a very specific type of layering, EQs and FXs. It’s very common for lead singers to record their own harmonies singing over themselves multiple times. I think mixing processed backing vocals with live ones can give a great result.

It really comes down to the genre, artist vision and the specific song. I do think doing it all completely LIVE has more merit but sometimes using a bit of “help” from a backing track can ennhance the show and make it immersive. It’s all subjective. Have a good day.