Does it have anything to do with not having to deal with change? The amount of coverage/protection/insulation ect. being consistent rather than changing with how you feel like dressing that day?
I catch myself, while shopping clothes, always for the same cut of clothes for the same reason, even going as far as getting cranky if the material/thickness of fabric I am used to is not available for the print I'm liking. Maby an extreme example...
But all the people I know personally who stick to either shorts or long pants come high or hell water tend to have a lot of traits where they either appreciate consistency or... no mainly that now that I think of it.