Liverpool never took this game serious since they have already qualify that's even why there betting odd was even big secondly they didn't play the game with some of there big boys if they played with their key players it would have been an easy win for Liverpool this is why PSV had more ball possession and more goal attempt in that game, Liverpool never saw that game as a serious one if it was a game that requires Liverpool to win and qualify loss and go home you would have seen how serious Liverpool would have been in that game I believe they would have play with all key players, let me just take Manchester City game and club brugge last night since Manchester City needed a win to qualify they put in all their best and also played with all important players to make sure they have all 3 points in that game and they won 3-1 so that's it, so In a normal circumstances it will really be a difficult one for PSV to win Liverpool in the UEFA Champions league game if not that Liverpool has already qualify.
A team resting their key players in league matches they appear on top, is very common to see in matches. Liverpool has an upcoming match to play against Bournemouth in PL. They prefer to win that match rather than playing their key players over the match they seem to have qualified in, round of 16(Champions League).
As Liverpool currently tops the Champions League table, It's gonna be a long time before they have another Champions League match to play. For the time being, their focus will be on mostly Premier League matches because they have a lot of PL matches in the pipeline
Exactly you are very correct there is no need risking key players in a competition have already qualify meanwhile you have important game at hand we have always seen such in football though all most all the couches have this display in common they always show no seriousness when they know that if they win or not they have already qualify to the next level that's why betting such games don't always move me because at that moment I don't always have confidence in them because they might decide to gamble with the game, if you watched Manchester City game yesterday against club brugge you will see how serious they were because they needed a win to qualify for the knockout stage and they won with a better scoreline.
Liverpool is really doing great this season both in their domestic league and the UEFA Champions league I believe if not winning this two I believe they will win the English premier league tittle.