It isn't just a mold concern, particularly in your climate (Colorado). Pumping warm, moist air into the attic is no bueno, dry climate or not.
I'm quite sure that your photos are from bath fan venting that either terminated within the unconditioned attic space or had poorly sealed ductwork even if there was a outlet outside of the building envelope.
The outlet of our fan ducts didn't end at the inside of the soffit or anywhere else within the attic space. It was taken completely outside with a vent cover on the exterior of the soffit. The soffit was unvented for three feet in either direction from that outlet. Any air that managed to come into the attic through the where the vented soffit began three feet away would have been minimal and
very passive movement and would hardly be considered "pumping" moist air into the attic.
In addition we typically don't even use the fans unless there's stink that needs to be exhausted out of courtesy for others in the house. The humidity from showers is welcome and dissipates rapidly within the conditioned space without being exhausted. Morning showers typically occurred with the HVAC warming up the house as well, so mirrors wouldn't even be fogged. After seventeen years there was zero evidence of moisture buildup under the roof deck of that house or anywhere else for that matter when it was sold.
