Do you realize the combined weight of 6 or 7 officers? That much weight on a subject could easily cause injury and perhaps positional asphyxia. Usually such resistive subjects are in an altered state, either mentally ill or high on a mind-altering substance such as cocaine or meth. This means that for all intents and purposes, they do not feel pain, so pain-compliance techniques such as pressure points and focused blows are ineffective.Therein lies one problem. Imagine a police officer under no obligation to risk injury? In a one-on-one situation, or two officers even, I can see the hesitancy. But groups of 4 - 6 still feel that's it too much of a hassle, or risk.
That leaves you with a pig-pile flailing around trying to wrench this person's limbs into restraints while he/she is actively resisting. This is almost certainly going to result in injury to the subject. Much better to deploy a Taser that will incapacitate them for long enough to get them safely into handcuffs.