Why are festival sets, esp electronic sets, so short?

Something has puzzled me, as an old guy concert goer who got into fests in the last 10 years. Why are the non-headliner sets so short?

I find that under 90 minutes is not enough for an artist to loosen up and get into the groove. If I ran a fest, I’d want to book fewer acts who play longer. Would probably be more economically efficient too, which would be good for artists, audiences and owners.

Thoughts?