Us Air Force fire dept gear?

Probably because their duties and responsibilities cover a wider range of things like dealing with aircraft crashes and and responsibilities from enclosed or small places more than what a civilian firefighter's job normally includes.

The silver gear is more effective against extreme heat, as would be experienced in aircraft fires. Pretty much ALL airport fire departments use similar gear.

They are dealing with aircraft fires mainly not building fires. Different type of fire different equipment.

Because the Air Force is cheap (well, broke is a better way to put it--thanks Congress) and many bases have decided to just buy one set of gear that can be used for both ARFF and structural firefighting.
My base finally just started giving out separate structural gear to its firefighters a few months ago.

USAF fire gear is also biohazard and chemical protective gear. Standard fire gear is only designed for fire protection.

air force firefighters do not fight structure fires( buildings )

they fight aircraft fires