No need for complex calibrations, expensive electronics, a ground crew to switch it to the right aircraft settings, no waiting around for missing said ground crew, power systems and so on.
You guys obviously haven't seen the hands-full of "shrapnel" that some of the more dedicated arrival crews pick up from the tarmac prior to your arrival. It's a brave man/woman who taxis to the gate without proper clearance from ground staff. On one sweep, I picked up enough metal items (bolts, springs, large ball bearings, etc) to spell the word "LOTS". There were also chunks of crumbling tarmac which also wouldn't do the core of your engine a lot of good. Fortunately, most of the metal items are from cargo trolleys (not from aircraft).