PWM is trivial to implement, but you can sell it for real money as a feature. Or, in this case, a "feature". Not that it wouldn't be easier to just wire the door switch into the power rail for the internal lighting, but then it wouldn't also be able to play a cute jingle and tweet Elon Musk when the door opens.

Regarding slow starts - not that it's terribly useful to mention now, I grant, but most incandescent appliance bulbs can be replaced with compatible and much less temperature-sensitive LED ones these days.