From Reuters:

Unelected Supreme Leader Ayatollah Ali Khamenei, among the first to vote, told Iranians they would be endorsing not just their chosen candidate, but their country’s Islamic system.

“Whoever you vote for among those seven candidates, it’s a vote for him, the Islamic republic and the constitution,” he said after using a special ballot box at his official residence.

That is exactly why such a drove of people are planning on avoiding the ballot box today.