UFC no longer structures cards from most to least important. They haven’t in years. I personally disagree with their philosophy, think more important fights should be featured higher up on the card. But it is what it is, I watch all anyways.
This is a misleading talking point that you see get thrown around - they absolutely do care about card positioning, because they are not complete mongs, it's just not 100% linear (e.g 'feature prelim' being an important slot). And they are also lazy (thanks ESPN deal) so they often just don't care. But heirarchy is still a thing.
Does Paddy Pimblett randomly fight on the prelims now? No. His last fights have all been on PPV and have all been scheduled in that 3-4 spot on the main card (with one getting bumped to co-main after an injury). They haven't initially scheduled him for main/co-main bury him in the type of prelim spot Evoleov-Sterling is on, because they are not stupid.
One thing they have actually been doing since the Zuffa years is burying fights where they don't want to promote the winner - in this case they don't want to spotlight this fight to force their hand for a title shot. This is clearly what is happening here.