Righteous Zeal, once one of the hallmarks of the Black Templars has fallen on hard times.  Formerly a way to make your opponent pay for killing a Chapter brother by giving us a free way to get closer for that short ranged firefight and/or assault, then a way to sneak a +1 cover save (voluntarily GtG, then RZ out of it) pre-FAQ and now merely a way to get an extra d6" move between the opponent's shooting and assault phases, if you really want to move.  Hence, it resembles Righteous Mild Enthusiasm more than Zeal.

What kills many lists, especially more competitive mechanized ones with our overpriced codex, is that Commanders are less attractive for the points spent.  This opens up a loophole for your opponents since if you take even one casualty, you must take a morale check at the end of shooting.  Not even IG has a chance to fall back this easily, you at least have to kill two or three of them.  Yes, it is true, you will make most of those checks, but the fact is there is still a 27.8% chance a Ld8 unit (like our Crusaders) will fail and fall back.  Many times this is just annoying, but sometimes it can be devastating, especially for a gun line list that is trying to maximize its range advantage.  Even if they set up 7" away from the board edge, if they fall back, there is a 58.3% chance that the unit will be eliminated if it falls back since you only have to have one model "contact" the board edge to eliminate the entire unit from play when falling back.

Combined, that is a 16.2% chance that any Ld8 unit in a Black Templar list will flee from the battlefield if placed 7" away from the edge.  It drops to 9.7% for Ld9 and 4.9% for Ld10, so even with a Commander, the risk is still there for a very limited benefit.  It also gives a tactic usable when facing a Black Templar army without a Commander of simply shooting as many infantry units as possible.since for Ld8 units at 7" of the table edge, it is pretty much a 1 in 6 chance of killing the unit if you kill one model.  Not bad for a bit of plinking, is it?