From ODOT's McKenzie Pass update:
"
We do not open the road early for hikers or bikers before its open to vehicles, it is either closed or open to all. Signs are posted and gates are locked when the road is closed." and "People who choose to bypass locked gates and closed signs to access the road when it's closed do so at their own risk."
It could be there have been some issues with people crossing the gate when they were working on the road, or possibly people have crossed the gate unprepared and ran into issues. It's also possible the statements are for protection from legal ramifications if someone were to get into problems or got hurt. No matter the issue, be aware when crossing the gate to make sure they aren't currently working and be prepared...
https://www.oregon.gov/odot/regions/...e-highway.aspx