It's the same reason most team play this formation, it's in fashion. Conte plays this formation and people saw that it works for him so they copy it to try to find magic solution that's going to solve their probelms, e.g. Stoke, Arsenal. If 3-5-2 was the best formation for Stoke/Arsenal Wenger/Hughes would have be playing it for years and buying players to suit that formation. Instead they just follow the trends, they'll be wearing skinny jeans and getting peaky blinders haircuts next.