Does it HAVE TO BE? No
However common sense dictates the SOP be available to anyone with a need to know so they can properly do their job.
What good is an SOP if it cannot be accessed in a timely manner?
There might be one exception. If the SOP is classified then access could be curtailed based on security reasons.
This is an issue that should be addressed with the chain of command and seems like an incredibly easy fix.
Hope this helps