The run-in is frustration. Because of the sea of injuries you had the replacement players being knackered and the returning players being undercooked.
Look at the teams we dropped a point to since having the league in our own hands with 7 games to play;
Manu - They're fucking shit
Palace - They are in good form but we were at home
Everton - They're shit
West Ham - Are in dreadful form
We did well to challenge for the league given our injuries but what a missed opportunity
I know its been talked about the players who returned not being up to speed nor making much impact, but I think in explaining what has happened over the past month goes beyond that. We have been teetering on the brink all season. The chickens came home to roost is what happened.
Maybe five games in total, all comps, where we have been comfortable? The Newcastle game, battered for 75 and overrun in midfield, they should have been out of sight but after upping the tempo and energy in personnel (Endo and Gakpo off, Nunez and Elliott on) we pinched that game late on. At Palace we were again outrun, and but for a soft red card we never looked like getting back into the game. Home to Fulham, behind 3-2 after 86 minutes, then won it with two late goals. Brilliant comebacks of course, but you don't want to be having to constantly go to the well, which we have done 23 times. Comebacks should be the exception not the rule.
Three of the four results before our downturn in results: last second winner at Forest (around 75 minutes they had a glorious chance to go 1-0 up themselves when it just went low past the post), 2-1 win home to Brighton (Lallana's shot to make it 2-2 a couple of yards past the post), and 3-1 home to Sheff U (Mac special to put us ahead with 15 to go). We hadn't been convincing at all. Credit to the players for getting through them though.
When we then entered the business end, when the pressure ramps up, that's when the cracks are exposed. That's when the solidity of a team really is tested. But this is a ropey outfit. The two games against a dreadful Man U, we conceded six. That big pitch at OT needs a very athletic midfield, but we left gaps galore, space a toothless attack could exploit. One hopeful looped ball over the top by Casimiro, no DM in sight, they were in. Slow, flaky, weak, exposed.
So the pressure being ramped up which exposed the cracks there all season is one reason for the downturn in results. The other, namely Atalanta, is the higher quality opposition the further you go in a competition. We were taken apart by them, with every weakness, lack of athleticism in midfield, the sloppiness in full backs (Tsimkas and Gomez), pounced on.
Less than 72 hours later the season effectively ended vs Palace who in the first half took full advantage of the lack of athleticism in midfield. The tempo and energy ramped up in the second half with Endo replaced but this late in the season with so much riding on every result the pressure got too much and we couldn't rescue yet another game. Had that been the 3rd game of the season there's every likelihood those players don't snatch at the chances we had.
Basically increased pressure, and a higher quality opponent, is what undid us. Jurgen would have needed another window to address the deficiency in athleticism in the team as we have been far too open in midfield where games are largely controlled. Have no doubt had he stayed he would have done so.