The main reason is that people are paying these amounts, hence the market price rise. I would think it is for nostalgic reasons and builds that are trying to stay period correct.... they do pull on my heart strings a bit and bring me back to the days of 90s Japanese drag racing at Central circuit where they were common, they sound pure evil too.
Can you buy a far better turbo? Of course you can, but that's not the point of the price rise.