Why do elite/advanced deadlifters often fail the rep during lockout?

For me and hopefully for literally everyone else ,The starting position of a deadlift is the hardest . Once the weight has been lifted a couple inches of the ground , theres no chance the rep is gonna fail from then on . But i see a lot of videos where elite deadlifters struggle much more during the lockout phase compared to their initial lift . It doesnt make much sense to me