A hell of a lot of people not understanding...
People buy these type of plates as an investment.
It's like buying a piece of art, Picassos don't sell for millions purely because of artistic quality, they sell because in a few years time they will sell for more. Same with an 80 year old bottle of wine, or shares in google, or half a ton of gold bullion, or another house...
Once you've got as much cash as this guy you want to spread the risk, especially with an impending recession when the stock markets and property are likely to lose more value than art & trinkets. A number plate is just as worthy as any other investment even if it is worth more than my house and car put together.