Because it's the only bank that doesn't require a mailing address and I don't have a mailing address.
In US, for example, their addresses are classified as Commercial Mail Receiving Agencies, and have a "Commercial" address designator. USPS has an API for that. If you get a bank to accept this address somehow, then the next trouble comes - they're gonna ask for utility bill for address verification and you can't have any utility bills for it.