There is a huge misunderstanding about Expected Goals.
Name an elite team that is performing well this season (Man City, Liverpool, Dortmund, Barcelona etc etc) and you will see that they are massively out-performing their expected goals numbers. In the table linked, green is better than expected, red is worse.
https://understat.com/league/EPL/2018
Likewise, the teams at the bottom of the table will typically have been a bit unlucky, missed good chances to score in some tight games they ended up losing or drawing.
It's not just this season, it is true of most seasons. When Chelsea won the title under Conte, their expected goals for was 61.80, yet in reality they scored 85. Their expected points 75, in reality 93. Spurs finished 2nd. They too massively out-performed their expected numbers. City last season scored 14 more than expected, and got 9 more points than expected.
This may comes as a huge shock to you but elite players when performing well tend to finish chances at a better rate than an average player would. Elite keepers save shots that many other keepers wouldn't.
If you go through the individual games, Expected Goals didn't like the performances against Spurs and Leicester, matches in which United scored in the first half then sat deep and defended for the rest of the match. In contrast, the Burnley game in which we were 0-2 down, looks like it should have been an easy win for United as we created several big chances to score.
Based purely on chances, the Fulham match could have been a draw, yet anyone watching will have noticed that Fulham had several opportunities in the first 10 mins then almost nothing until the score was 0-3. Ryan Babbel's big chance after 76 mins when he hit the post from close range, was worth 0.59 xG (on average, out of 100 shots from that position, you'd score 59 times). Yet even if he had scored, Fulham would still have struggled to get a draw in the time remaining.