Do parents feel safe engaging with school?
Is there something holding them back?
Did they have a past experience with schools that was negative?
Do cultural norms keep them away?
If you are not able to interact with parents, it may not be what it seems.
Give the benefit of the doubt.
Make the extra effort.
Find alternative opportunities.
Do everything you can from your end without placing any judgment or blame.
Connect in any way you can.