Why
Well, personally I wouldn't. UBZII is not useless for shoes, it (along with all unbalanced counts used in running count mode) is useless for shuffle tracking, where it is necessary to know the true count.
The only problem with UBZII and shoes is that (again, like all unbalanced counts used in running count mode) it tends to understate the advantage early in the shoe and overstate it late in the shoe.
Despite this, it works pretty well "out of the box." Still, if I were going to concentrate on shoes I probably would use a true count conversion.
I was certainly not suggesting that everyone (or anyone) should switch from UBZII to Zen, I was merely pointing out that, if one wished, for whatever reason, to switch to a traditional balanced count, going from UBZII to Zen would be a fairly simple matter.