As well as contact, it's probably a way of giving notice to as many as possible of the situation as the lender or their agents won't know who is or has been living or staying in the property themselves.
There may be other family members, tenants (possible without tenancy agreements, the property has been let without the lender's knowledge) and all kinds of other people staying.
There is also the risk of squatters if the owner being repossessed has already left the property.