Why do many musicians not get any credit at all for producing backing music, whearas Avicii and David Guetta etc. are primary artists even on their vocal’d tracks?
Firstly, producers and backing musicians do get credit, even if they aren’t the featured artist (check the album credits). Secondly, in your example David Guetta is the featured artist who is known for the production, while the vocalist is just a contributor. It’s also a genre thing, in EDM the focus is on the producer and not the vocalist while it’s the other way around in pop music.