Well, the way i see it there are a couple of issues. The person has to get something from the instance. There is a reason things like slabs are no longer run, because the vast majority of 70s will get absolutely nothing from it (now if they had a plan such that the 'easy' heroic was as hard as the normal end-game, that would help).

The second thing is that you can't expect a burned out raider with a T6 geared toon to want to go back and do heroics, there just isn't enough reward. But if that person had a new 70 alt, sure they wouldn't mind doing heroics/kara, b/c they will get something out of it. For me, my main really wont get much out of a heroic or any 5man or 10 man. I'll do it to help friends/guildies (like tonight, we are doing the Champion of Naaru for a guildie). My newly 70 druid would kill to do any sort of heroic 5man instance though, she badly needs the gear.

I'm not sure what the answer is, but the guild needs to have good communication and a cohesive structure, and offer useful rewards. (IMO)