Question

Why can’t a pace or a footstep cannot to be used as a standard unit of length

Answer 1

These things can not be used as units because the measurements of these things are not precised. A tall man's footstep is not same as the footstep of a short man. If we use these things then we will face many incorrections.

So, We use ‘metre' as standard unit, because it is pretty precised and is available everywhere in the world.