It's a condition of Juggernauts as a whole.

All of them bar Mordekaiser have two thing in common: Stickiness, and lack of hard engage. The best they get is a burst of movement speed, but, again other than Mordekaiser, once they are on top of someone they stick to them while boasting the highest combination of damage and tankiness in the game.
Notice I included
and did not include
because, despite riot categorizing them as vice versa, Shyvana has more traits of divers (burst+sustained damage and heavy engage without any form of disengage) while Olaf has those of Juggernauts (stickiness, "running a target down," almost entirely sustained tankiness and damage).
Put in other ways, Juggarnauts can be compared to the other figher class, divers, as well as to the two tank classes of Wardens and Vanguards.
Divers offer: Engage, middling damage, middling tankiness, middling cc
Vanguards offer: Engage, high tankiness, high cc
Juggernauts offer: Preventing disengage, high damage, high tankiness, weak cc
Wardens offer: Preventing engage, middling damage, high tankiness, middling cc
That preventing disengages is what I referred to earlier as "stickiness;" once a juggernaut is in a fight it's hard to get away from them, the tricky part for them is getting into the fight in the first place.
This dichotomy is a bit more comprehensive than just "crowd control" "ally buffs" and "damage" because two classes that offer damage can do so in drastically different ways
FWI I'll also dissect Assassins for contrast
Assassins offer: Engage, disengage, high damage, weak cc
This is why
is classified as a Diver, because no matter how fast he kills someone, he still doesn't have a way to disengage after jumping in and taking someone out. Same with
's tiger form having such a powerful kill potential.