That's addressed here:
The escalatePriority API is offered as a static method on Task in order to slightly hide it away from using it accidentally by stumbling upon it if it were directly declared as a member method of a Task.
In other words, I'd rather people not "stumble into it by autocomplete" and then figure it's a great idea to actually call them. Most people really have no need to call these things and at least by putting them a little bit out of the way I hope to signal that in ways other than their documentation (which also indicates "you probably do not want to use this API")