A club can do well in a league and does bad in another league and that how it has been happening in the football sport games. Liverpool which doing well in the English Premier League and not in UCL. And that is why they are using all their might to make sure that they win the trophy in the EPL. And the gap Liverpool gives to Arsenal in the EPL is good for them to win the league and if in case they didn't win this league, they will not win another league in another season again. This is a good opportunity for them and they have to win the title.
Liverpool was actually doing well in the Champions League untill they were unlucky on the day it mattered the most so it wasn't like they haven't been doing well at the champions league, literally they were at the top of the table at the league stage and so they were even perceived to turn out a very strong contender at that point but then they got unlucky and crashed out but now the premier league is the only hope for a trophy this season. Arsenal has gat almost no chance at the Premier league but they do at the champions league so they can go ahead to put in the effort and possibly get an opportunity to likely get the champions title hopefully even with the strong opposition they will be actually facing.