This is why I do not think that it would be really that hard to understand why people think that they would be the most liked one, because they are Barcelona and they have a magnificent history. Just 10 years ago or so they won 6 cups in a single year, that is not really that common, only Bayern did that after them I believe. I know this is not reflective of current season, but it is reflective of the "idea" of Barcelona in people's minds.
If we look at how Barcelona faced Galatasaray it was quite difficult to win, this makes some people doubt Barcelona to go further in the Europa
League. It is true that there is no 100% guarantee that Barcelona will win the Europa League trophy, but because the Europa League is the only
trophy that Barcelona can win this season, I'm sure Barcelona will try their best to win it. And seeing Barcelona's increasingly consistent form
in La Liga, then how Barcelona finally won the match against Real Madrid in La Liga, makes me even more optimistic that they can win
the Europa League. Moreover, Barcelona's next opponent is Frankfurt, which in the Bundesliga competition the game is inconsistent, then when
facing Betis previously in the second leg, it can also be said to be lucky because Betis players made an own goal. So I think Barcelona can beat
Frankfurt and get to the semifinals, because like you said Barcelona have a very good history as a big team, and they will prove it by winning
the Europa League trophy.