I've been scouring Lodestone for the better part of 40 minutes and I can't come up with the answer (so it may have been in an interview, but I'm fairly sure it was not).

This is what [something] said in a paraphrase to the best of my recollection.

The reason you must wait for a reset to re-issue failed leves is so players don't fail them on purpose and re-issue them immediately to continue to grind SP on leves.
That statement says to me (and mind you its a paraphrase, I can't find the quote or I'd be planting it in ALL of these threads everywhere) that they were aware upon implementing Guildleves that people would fail them to grind SP rather than accept the rewards of Gil & Faction Points, so they made sure there was a limiter in place (of 36 hours).

Therefore, they are aware of it and compensated for it already. No further QQng needs to flood the forums. There's no need to misconstrue my paraphrase to mean they don't WANT us to fail leves. They simply didn't want us to fail & retry immediately. 36 hours is enough of a wait according to SE in some mythical post I can't find.

As a contrast, I'm pretty sure in Beta or Alpha you could reissue failed leves much faster than 36 hours. (Maybe it was a post on the Beta forums? Man, idk).

I'm sorry I can't find it because it would be great to throw down on the table whenever this pops up 1/week.