Dungarees were a heckuva lot hotter than BDUs. Plus, since everything is always being painted, one misstep and those dungarees are ruined. With the BDUs, haze gray just blends right in. Helps with morale as well, since now sailors can actually look like they are in the military, rather than prison.
I've wore both the Navy dungarees 4 years active Navy and wore Army Fatigues when I later went in the Army NG's.. No Contest as to which is cooler and more comfortable. Dungarees are by a long shot especially with a short sleeve shirt. My 1st Class, Chief, and Division Officer expected my uniform I was working in to be well seasoned in grease and oil stains but clean. It's not hard to tell the difference. It meant I was doing my job. I kept an extra set or two for going off ship on the base or Field Day inspections etc.
Now if the Navy wanted truly functional as well as comfort and stay in tradition Dickies and makes some fine light short sleeve coveralls in Gray and Navy Blue. I wore them in the 1970's when I was T.A.D. to the Liberty Boat Crew. I wear those type of coveralls now as my everyday clothing.
Abandoning traditions is part of what started the morale troubles in the 1970's. They changed dress uniforms so when you boarded a plane you were asked "hey sir when are we taking off?". The did away with Bosuns whistles and just about every tradition the Navy had up till then. It failed! So did morale. By late 1979 early 1980's the crackerjacks were back as were Bosun Whistles and most other traditions. The Navy dungaree working uniform was the longest running Navy working uniform. The pants also made decent life preservers if you got tossed over the side.