I think this is a big part of it. Permanency in earlier editions was effectively a "spell resource and action resource" tool - it let you have up spells not from the current day's resources, and in some cases let you have up otherwise short-lasting spells without taking the action to cast.
But now, with Concentration as a limiting factor for many buff spells, it changes the equation. Other ways to get around the spell resource part, such as potions, now require the drinker to maintain concentration. (Which might still be worthwhile if they had nothing else to concentrate on.) But permanently requiring concentration for any spell that uses it might be more limiting than useful, but not requiring it would be more broken then balanced.
I haven't looked at the non-concentration spells to see how they would fare. But I'd say leaving out permanency from the first list of spells was probably intentional. And my guess is that Contingency is more likely to come back then Permanency.