It doesn't matter how good of a DRG you are.

[Docent]

Heavy Thrust had most likely worn off by that point. They probably wanted to reapply it before performing any jumps as it's a DPS loss otherwise. I don't know how far away the main group stacks from the tank in your team, but it mine it's not far at all. It takes less than a second to run to Nael from the stack point. It makes much more sense to run to Nael, apply HT, and then go through your rotation and jumps rather than use an unbuffed Spineshatter Dive to save less than a second of walking.

As a main MNK who dabbles in DRG, I think this illustrates one of the biggest difference between monk and dragoon as far as gap closers go.
As MNK, I shoulder tackle whenever I can. The cooldown is short, and I can't actually wait for GL3 and all my buffs to be up to use it for "max damage" because of the minimum range to use it. Heck, I LOVE it when bosses have knockbacks (unless you need to save the stuns) because of how fast I can zip right back to it as if nothing happened.
As DRG, Spineshatter Dive is a bit more versatile and I find that it is often on cooldown when I'd like it to be up, probably because it fits in the normal damage routine. Same goes for Dragonfire Dive, really.

Hats off to all the good DRGs. You guys actually have to think a lot more about your things than I do as Monk (All I need to really pay attention to is how I can avoid sacrificing myself to the Greased Lightning Gods) :P