I realised not all people on the island in The First Purge wear contact lenses but want to commit the purge, like Dimitri. Why is that?
The rule was, to get paid or to show their maximum involvement, citizen's should wear the lenses. But Dmitri never planned to go on purge for some financial gain. That's why he didn't wear the lenses. People who went to purge intentionally and wanted to get the prize money, wore the lenses.
I saw the movie sometime back so I clearly cannot remember the scene, but when they give the purge kit (lense box & the blue flower etc.) to Isaiah, they mention the rule.