Why do some guys work the brush hard face lathering and some not at all?

Yes, barely bending the bristles, dancing the tips vs working the knot. The knot, hairs midshaft and proximal to the handle hardly bent at all, solely supporting tips.  Pressure against face is virtually nonexistent.

Reflecting on this, may explain why disfavour synthetic knots lacking the backbone/density of a high quality badger...employ zero splay. 

Hence working soap versus working knot