I've often seen this perspective shared as you've offered it here, but at some point, I began to consider an alternate perspective on it.  Perhaps instead of the other crabs attempting to keep the one crab back, perhaps the crab was inviting others to hold on so he/she could help them get out to. Unfortunately, they weren't strong enough to lift all of them and hence didn't make it out either.

As in life, sometimes we make progress and want to help others make progress too. Unfortunately, in our effort to help others, we overextend ourselves and fall back into the same pit we were trying to climb out of.

I'm not saying either perspective is right, or wrong, but that there are other ways to view the situation.