I think it's not so much a question of material degradation due to humidity. The problem is low outside air temperature (-50 deg celsius?) leading to low inside surface temperature leading to condensation which is also a problem WRT cables routed through cabin walls.

Maybe inside surface temperature on carbon fibre is higher (better insulation), allowing for higher dew point [1], thus higher humidity levels.

[1] https://en.wikipedia.org/wiki/Dew_point