Because they bring good sides down to their level. It's what Jose does.
TOP SIX RECORD AGAINST EACH OTHER
Pos Team P W D L F A GD Pts
1 Liverpool 10 5 5 0 16 9 7 20
2 Chelsea 8 4 1 3 14 11 3 13
3 Tottenham Hotspur 8 2 3 3 9 9 0 9
4 Manchester City 8 2 3 3 10 13 -3 9
5 Arsenal 8 1 3 4 13 16 -3 6
6 Manchester United 6 1 3 2 4 8 -4 6