Perhaps (any of these can be true, or false):
- He wasn't the only one pushing it? Lemay was described in Bloomberg as one of the key people behind Liquid Glass
- The vision wasn't as bad as it turned out to be, but it was rushed because of yearly releases and Apple having nothing to present?
- None of the senior leadership use the devices beyond occasionally, so they couldn't care less what's happening to the UX?
On your first point, I don't know if Lemay merely agreed to keep his job or was an enthusiast of the vision. But it is a bit worrisome, if Bloomberg is to be believed.
On your second, Liquid Glass is merely the culmination of years of bad direction. Hiding essential feature on hover (notification's close icon, elapsed time on Apple Music, proxy icon, etc), poor contrast, legibility, background/foreground differentiation, was a long running process.
On your third point, I think it's possible and, if that's the case, deeply troubling.