PDR
Why is it any different for pilots?
.. Because the law says so and as xollob has said it's all about the legal restrictions on pilot's working hours.
As a pilot in the employ of an airline you usually have a nominated home base (e.g. LGW). Getting between home and base is down to the individual ( and I think that's what most mean when they refer to "commuting"). The timing of that journey doesn't count as Duty time because it's construction (time of day, time of journey, means of travel) is down to the individual.
OTOH if you are at your designated home base and the
employer decides to send you elsewhere to start a block of work (e.g. "we want you to go from LGW to CDG and operate out of there for a few days ) then that journey is usually regarded as "positioning" (or "dead heading" ), is organised by the airline and traditionally/legally it's regarded as part of your regulated duties and so the hours spent doing so count against legal limits - because it is being done solely at the behest of the operator.
I know it can sound like semantics, but the devil is in the detail - especially if the regulator(s) gets involved...