They are not. In 24 states the electors have to vote for who the state elected. The electors cannot vote outside of what the state tells them.
By 1796, the first contested presidential election, parties expected their electors to vote as instructed. Today, electors chosen by the parties are usually extremely loyal members who would never consider not voting for their man.
Legal Requirements or Pledges Electors in these States are bound by State Law or by pledges to cast their vote for a specific candidate:
ALABAMA
ALASKA
CALIFORNIA
COLORADO
CONNECTICUT
DISTRICT OF COLUMBIA
FLORIDA
HAWAII
MAINE
MARYLAND
MASSACHUSETTS
MICHIGAN
MISSISSIPPI
MONTANA
NEBRASKA
NEVADA
NEW MEXICO
NORTH CAROLINA
OHIO
OKLAHOMA
OREGON
SOUTH CAROLINA
VERMONT
* VIRGINIA - 13 Electoral Votes State Law - § 24.1-162 (Virginia statute may be advisory - "Shall be expected" to vote for nominees.)
WASHINGTON
WISCONSIN
WYOMING
How many of those did Zero win and how many electors does that add up to?
All that is fine but has no bearing on the Constitutional issue. Presumably states could refused to certify the vote of rogue Electors but that would not stop the activities required by the Constitution and federal law.
Advisory laws, expectations, pledges or hopes have no bearing on fact that the US Constitution says nothing about how Electors will/must vote only that States can appoint them any way they wish.
Electors are elected by the popular vote but after that they are not under any other control. A state could presumably remove them but there is no mechanism to replace them since state laws have them elected by the popular vote.
It would be a nightmare particularly if there were parties controlling the legislature which differ from the party of the elected electors.