Why don't Heroes immediately respond?

The recent WoC HM difficulty forces me to revise the way I play PvE. It's no longer rush the group. Rather, I make my heroes set up a spirit wall, then pull, prioritize targets etc. Tedious, but Hard Mode is supposed to be...well, hard.

But what bugs me is that my heroes don't immediately respond to my flag commands. If I see there's a danger of getting wiped, I retreat and flag all my heroes back. But usually some hesitate for several seconds before obeying me...and end up dying as a result. Needless to say I have no sympathy for them . And I checked - there are no cripple or other slowing hexes etc on them.

When I tell a hero to go somewhere, I expect him/her to drop asap and RUN like their ass is on fire. No hesitation, no "finishing up skills". If they're in the middle of a skill I expect them to cancel it.

But they don't always respond with the alacrity I want them to. Does anyone know why?

Maybe they don't know what "alacrity" means. Next time just ask them to "respond faster" and see if that works.

As for the "why?"... it's a stupid answer, but that's just the way it is, I guess.
I have seen it as well, but I found the biggest problem is that I myself lag sometimes
What I mean is, you shouldn't doubt whether or not to run, just run; when you sense the wipe coming, don't wait until very last moment to flag away your heroes.

I also noticed that when you just flag them, heroes usually stop what they're doing. However, while running to the flag, they might stop running to cast a heal and then continue (this might be my imagination). So what I do if a hero needs to get out asap, is I take his flag and put it away several times (on about the same location). (kinda like when you are fleeing with your mouse and you keep clicking the the ground before you)

Heroes have an intended delay to their actions and also it helps save processor cycles by not having them check their action queue faster. I am sure it also helps reduce server load as well. The big reason is really the intended delay though which is to make it worth grouping with real people as they don't suffer the same issue.