If they only picked items with tons of likes and shops that were already popular then the feature page would be pretty toxic and a huge bulk of the apps sales would only go to a very specific handful of sellers. I also think they pick items ahead of time so if something gets sold before feature time they have to find another listing to fill the slot (but I don't work at depop so I could obviously be wrong about that)

Based on my expierence from being on depop for 7 yrs and being on the featured page every once in a while. For me they've picked items that weren't getting as much traction but were still unique/ different than other items on the app. Hope this helps