Why do we accept some instruments for solo work but not others?

I saw a comment on a website a day or two ago that made me think. Somebody had essentially trolled a video online asking "when is the rest of the tune going to start" before stating how they'd downvoted it on the grounds it should have had more instruments.

We're used to hearing music that is just piano, or just guitar. But I do wonder if we should look at music with less stereotypical ears. ....whether its bass guitar, keyboards, flute or synth etc

Thoughts?