This seems to have been the problem, according to advocates. They're saying that people weren't really clear on what the measure would accomplish.
I think a solid piece of evidence is the vote count. The total vote count appears around 300k less than all of the other measures, meaning people just skipped over that one which is never a good sign.
Ps. I just did spitball math at 6am, I didn't read that anywhere so totally my (could be wrong) observation