The very likely reason they didn't follow that procedure is that they didn't recognise the failure as runaway trim, which in turn is likely related to the apparent fact they didn't know MCAS existed. So couldn't know that the behaviour they experienced was what MCAS runaway trim felt like.
I don't think it's wise to speculate, but the stabilizer is coupled to a very large trim wheel in the cockpit that both audibly clicks as it spins and is market with white stripes (on a black wheel) to make the movement apparent. It's possible the pilots didn't realize what was happening, but it's not as if MCAS was silently causing a runaway.
