Casual players like having something to "do." The problem with sprint-less gameplay for them is that they spend a significant amount of time "walking," in their mind doing nothing, especially on big maps. The frustration is compounded when/if they're killed without a fight.

So even if the time to get into a battle is comparable, sprint lets people think they're doing something. That's the reason it was introduced to Halo and will remain in it until the very end despite how it screws up "Halo-esque" gameplay.