Because deadlifts are honest. You can't bullshit yourself with deadlifts.
Squats you can go short of depth, bench press you can too, and a hundred gym-goers and PTs will tell you "well done." With deadlifts, you either pick the fucking thing up or you don't.
Athletic Club East - curing iron deficiency
Current trainees' best lifts: ♀ 130/72.5/160 at 68kg, ♂ 220/120/235 at 106kg