Warning: obvious statement incoming.
Sometimes people are in too much of a rush and harm themselves as a result.
Ever seen someone leave before rolls could finish on a chest? I have. Too many times. Meaning ever. If they waited a few more seconds they'd have had a 20% chance at the 25-30g crystal, maybe a 5g shard or the 10-20g vendor price, and of course the orb which isn't vendor trash anymore. 10 seconds for an average of 5-10g seems worth it to me. Sometimes it's longer because someone leave before the chest even opens so we have to wait for the auto-pass. Why not just tab out to look at the porn you were anyway? I'm looking at you, 1k DPS guy.
Back when the timer on HCoS was tricky and we were getting the boss down with only seconds to spare, the moments of time to loot corpses weren't worth as much as a OMG EPIC DRAGON NEED NEED NEED. These days we have plenty of time. Most heroics don't have timers like that anyway. Taking two seconds to loot the 1g off a corpse, plus some trash or cloth is worth it now that it's not preventing us from getting a OMG EPIC DRAGON NEED NEED NEED. It's actually pretty neat; you click sparklies and get gold. I wish real life was like that.
Many of the heroics have optional bosses; you can skip them and still get your frost emblems. Some people skip them. Some people don't. And some people are idiots.
Imagine that you're in an instance and everyone else wants to skip the optional boss that you want. Would leaving group help? Not really. You'd have to start all over again. Might as well kill the last one or two bosses, get your trash and triumph, and requeue as you would anyway. You can avoid the debuff too. Hm, 10 minutes of bosses you'll kill anyway when you requeue or 15 minutes in Dalaran bored?
Or imagine that you want to skip an optional boss. Would leaving the group help? Probably not. Most optional bosses are 5-10 minute delays. The debuff, 15 minutes. Or 30 if you're in the future. Which you might be. Spooky. 5-10 minutes of the wastes of time or 15 minutes of Dalaran?
Then there is the added bonus of the DPS who do this. If you're just doing the one per day for frost, just stay in for 5-10 extra minutes and avoid a 15 minute debuff and 10 minute queue. Plus having to clear whatever you'd already done.
Culling of Stratholme is a special case. If you're going to be one of those jackasses who leaves, try first asking if they've talked to Arthas yet. The odds are that someone else has already left and while the group waited for a replacement, Arthas has been glad to see Uther.
Two seconds of reading while autorunning are worth 10g
I've said before to compare vendor and DE prices. Do it. Wait a second before picking DE to see what an item vendors for. Blue weapons are not worth DEing. BLue gear cloth usually is; blue plate and mail often aren't. I can get shards for 5g or less while weapons are 12-15g. Simply reading the vendor price is worth 10g to me. That's about as close as you can get to free gold.
Slow down, get rich faster.