Because the room was set up with a 3wire receptacle?Maytag Stacked Washer Dryer Pair: LSE7804ACE
Power hookup was via the old 3 wire setup (Hot / Neutral / Hot)
Until you change the wiring from the panel it won't matter.I have not yet obtained a 4 wire cord and outlet...
Best to just leave it be. Or put it back the way it was.
Read the manual to see exactly how.