Doing some market reserch

[IRISHMAFIA]

To me, the only logical answer is "other".

We would all love to have a locker room available, but that isn't always going to happen.

And we would all love to routinely go from our home and walk on the field to start the game, but that isn't always going to happen. Same with our place of employment (real job).

Some of our cars ARE the locker room and dressing there is not unusual, but it isn't the preferred location and sometime, far too open to the public.

Umpires get dressed in the location which provide the most comfort and ease available to them at that point in time. I believe that is the only real answer.