#3 The lack of recent success
Of course, one of the reasons why Liverpool and Manchester United teams of the past would have taken the game to their opponents is due to the fact that over the course of the last few decades they have been two of the best teams in the country, and in Europe. Liverpool dominated domestic matters during the 1970s and '80s, while United took over the mantle in the decades that followed.
However, both teams have been eclipsed in recent years, and while United still come to terms with the retirement of Sir Alex Ferguson, Liverpool remain in search of that elusive first Premier League title. Both sides have had their relative struggles in recent seasons, and it is inevitable that their lack of glory has made an impression on their negative approach to such key games.
Success breeds confidence and belief, and until the major trophies start returning to Anfield and Old Trafford respectively, questions will continue to be asked about their future direction under the guidance of Klopp and Mourinho. United have made the better progress in recent years, but they are no longer automatic favourites for the title, while Liverpool appear to have reached a significant stage in their recent evolution.
The question for Liverpool now is about how much further Klopp can take this team without massive investment, and the focus in each transfer window tends to be on keeping key players rather than signing more. To really move forward, new ownership may be required, but the big spenders of the Premier League are now on a different level to anything known before.