"Experienced", in so many cases, seems to mean they got away with making bad decisions multiple times in the past. If you don't have a brain (and use it), experience means diddly squat.
"They knew the weather was getting bad ... They needed to get back to their car and needed to get out."
No, they didn't. The world didn't end when they died/nearly died, so it wouldn't have ended if they were two days getting back to work.
"... the three were about a quarter-mile from Camp Muir when they got lost in the zero-visibility weather ... 'They spent a lot of time wandering around trying to find their way back to a camp or a trail ... But they couldn't find their way.'"
I live less than 60 miles from Mt. Rainier. The weather changes fast, but not THAT fast. Look to see what the prevailing wind is bringing. If you can't see what's coming, stay put. But it was just a day hike, so they didn't bring a compass, or know how to use a compass. No GPS either, I assume. A couple of El Cheapo survival blankets might have prevented much of that moisture from being absorbed into the down garments.
But all these 'experienced' hikers and climbers always want to travel light, don't they? After all, it's only a day hike.
Western Washington has had one foot in winter all spring. Snow was predicted on June 6 (up to two feet) through June 11 in the Cascades. What part of 'check the weather' did they not understand?
Sue