He couldn't fund the debt on Nederland because he had no cash. Having $1bn of assets is meaningless unless you sell them, which MJ was always reluctant to do.
Do you understand how a mortgage works, it's based on lending money secured against an asset.
If Michael had assets worth hundreds of millions if not billions then securing a loan for a piddling $40m would have been a piece of cake.
But if he's already mortgaged his assets up to the hilt and very likely beyond, then even Wonga would have refused him a loan.