I would be very tempted to place a bet that nobody in the decision making chain used Vista or Compiz to any degree.
Commercial software coding glorifies denying anything older than 10 years exist outside of museums, let alone learn anything from it. The same has merely infected design world.
But they did use early builds of liquid glass and that should've triggered nausea and someone must've said "Don't"... yet they still did. You don't have to have gone through Windows Vista time to understand UI/UX (least of all, Apple Designers).
Is this known to be true or speculated? I don't know how this process is handled at Apple specifically, however, generally decision-makers are highly detached from UX. One would think that, especially for an overhaul initiative, "important" people would daily-drive dev/nightly builds to wear off the cool factor and experience the not so pleasant annoyances, but generally they shield themselves from that and mostly look at the "cool demos".
Regardless, as far as I am aware Apple has a tight product release cadence and ties feature gates to that. Obviously hardware readiness gates are much earlier than software, but I can easily imagine situations where "yes men" report "good enough" at gates relevant for marketing, feature gets greenlit, but then gets half-assed for the actual release. Recall iphones crashing at the initial release demo? Might as well be history rhyming.
Commercial software coding glorifies denying anything older than 10 years exist outside of museums, let alone learn anything from it. The same has merely infected design world.