Sure, a priority move means a change in plans, IF they lead with it.
The reason to taunt is because you as you said sleep last for 1-3 turns, but only the first turn is guaranteed. If you switch on turn one of sleep, then evoboost on turn two, then baton on turn three, it could work, but... unlikely. Depends on how many resets you want to do.
With taunt, you make sure they have to use an attacking move, thus knocking out purrloin so that eevee can switch in after the prankster yawn, protect during the drowsy turn, then evoboost the guaranteed sleep turn, and baton pass on the second sleep turn. Still runs the chance that they wake up after one round of sleep, but that is better odds at least.
Of course you could always attempt something else with your yawn lead, if they survive the first round. Yawn, sub, sub, baton to another set-up sweeper like Vivillion who can sleep them again and quiver dance.