Blank and void votes happen when voters don't fill out the ballot on this particular question, or something was wrong with how they filled it in or their ballot as a whole.

Blank/void ballots do not count towards the outcome of the vote, but they can tell us something about voter participation and rate of response to ballot questions, and also about how elections were administered.

There were 3,092,693 blank/void votes for this ballot question.

When we include blank/void votes into the picture:
Total number of votes: 4,294,063
Yes votes: 17.63%
No votes: 10.35%
Blank/void votes: 72.02%

Still, there only need to be more yes votes than no votes for a ballot question to pass!