Why do some vertical lifts not have guarding around the scissor pack?

This is usually because the manufacturer has installed alternative measures to prevent trapping in the scissor pack in line with BS EN280: Mobile elevating work platforms – Design calculations – Stability criteria – Construction – Safety – Examinations and tests.

Source: BS EN 280:2001+A2:2009 – 5.4.4: The downward movement shall be automatically stopped by a safety device in a position, where between the outer ends of the scissors the vertical distance is not less than 50 mm, so that crushing and shearing of fingers cannot occur. Further downward movement shall only be possible after a suitable time delay, giving the operator the opportunity to see, whether persons beside the MEWP could be injured, and a further command of the operator.