Naturally, he did it to earn money.
Now we know who taught Axl Rose everything he knows about managing start-up costs.
He was inspired to build his own giant boat in 1977, after chartering his first, less-giant boat for fishing trips failed to earn him any money. After concluding this was because his galley was too small to allow for truly hardcore fishing, he set out to build his own, ginormous fishing boat. That way he could charter more people for more trips and make more sweet, sweet mackerel money.
Reminder: He spent $2 million to get there.
Unless somebody catches the Kraken, good luck breaking even before the next supercontinent forms.
He also took 38 years to finish, because Dillon Griffith is not a professional huge-boat maker. What's more, he eventually moved away from the ocean and into a land-locked area, yet he continued to build his boat. That's like moving to Death Valley and trying to build your own ice hockey rink. Oh, and the project damn near killed him, and not in the typical "oh, all this hard work is killing me" kind of way. No, more like a crane fell on him once and shattered his body. That kind of killing. Also, an 11-pound cylinder once broke his neck. After that, it was probably less a labor of love and more one of pure stubbornness. He saw a ship that steadfastly refused to be built, and he stared it right in the barnacle-encrusted porthole and said, "Fuck you, thou shalt be built."