Why do you like to run low-level instances?

I see guild members of mine constantly trying to get groups together for low -level instance runs on their alts, as well as seeing lots of random LFG requests for various low-level instances and I'm curious why people are that determined to run their alts through these instances?

I'm not talking about a new player who wants to experience all the content possible, but rather experienced players who've already gone through all the instances on other alts. Why the urge to run it again on another alt when the gear you get will be obsolete in a few levels anyway?

Of course I understand you have to run end-game instances over and over to get rep or get certain items that will last a long, long time, but why bother running SFK or DM or SM multiple times on alts when you're just going to dump the gear in a few levels anyway?

I've leveled many alts and I just keep on questing and grinding. The only times I get groups are for key items like the carrot on the stick from ZF becaue it will last for a long, long time.

There is no need to flame as I'm not saying you shouldn't do it, but I'm just curious why so many people seem so eager to run these instances on every one of their alts?