Statistically, we all know that Manchester United dominated the match - they just couldn't score despite having several good chances. Arsenal only managed one goal in the first half and couldn't add another until the end of the match. Manchester United tried very hard - but unfortunately, they failed despite having 22 shots, 7 of which were on target.
That is the beauty about football. I recall Arsenal being in the same position Manchester United were in yesterday. They would play all their hearts out, only for United to grab a winner with some random late goal by off form Lingard 
Arsenal have been title contenders in recent seasons - but they haven't been serious. Liverpool have tended to be more successful than Arsenal - certainly because only Liverpool have been able to stop Manchester City's title-winning streak. Arsenal are a great team - but they haven't been able to win the Premier League title due to poor performances towards the end of the season.
They haven't been consistent enough. The only way of having an assured title win is to be consistent throughout the season and most importantly, convincingly beat all the top contenders