Playing for a bottom table side that focused on him as the main player and while also taking penalties.
There are a lot of Politanos and Giovincos that do well for small sides then fail to deliver when they go to a big club.
there're literally no wingers in Serie A that have been consistently as productive as Berardi for a decade. Politano and Giovinco didn't even have half the career of Berardi. so no, there are not a lot that do that well for smaller sides.
btw I agree that Berardi is not a good fit for a bigger club, it's what we see regularly with the NT where he struggles to be effective in a different set-up. however I see no reason to belittle him or his achievements, its not harder or easier to play for a smaller club, different people strive in different circumstances. Ancelotti sucks as a midtable manager and is very good as an elite team manager, Marotta is very good working on a budget and was wasteful when given more funds, Zidane couldn't be arsed to get his dick up for small games, but was magnificent when he wanted to play.