Assets are worth more to Venezuela than anyone else is willing to pay. In case of defaulting, creditors can takeover those assets cheaper than they could buy them otherwise.
Citgo was stripped of value last year by issuing bonds to pay a large dividend back to Venezuela. It is now so encumbered with debt that any remaining equity value is nominal.
Part of the reason was due to various lawsuits related to assets of US companies that had been nationalized and also to repatriate funds to support government initiatives.