People have tried that, and failed for various reasons:

• You can’t move the ship out of any port without insurance
• Insurance for a rusting hulk isn’t cheap
• No nation on earth will let you park your uninsured rusting hulk offshore, as it will pose an environmental and navigational threat to the area
• Even if you anchored outside a country’s 12 nautical mile economic exclusion zone doesn’t mean their navy/coast guard won’t bother you. They have maritime rights outside that area nonetheless.
• You’d still need to take the ship in for maintenance somewhere, and now all your regulatory problems begin again.