Because they can get that much, and also because they're all bronze and built to last 100+ years with minimal maintenance...the last toilet anyone would ever need to buy. People move 'em from boat to boat and leave 'em to their kids in their wills. Plus, as the price of metals has increased, it's driven the price WAY up in the last year.
If you think the price of the Baby Blake is high, the Blake Victory, the larger "throne," sells for a staggering 9999.99 British pounds, which converts at today's rate of exchange to just under $15,000 USD. Why would anyone spend that much? For the same reason they'd spend over $100k for a Rolls Royce. However, in the current world economic situation, people may not be buying many of either one.
The original Wilcox-Crittenden Imperial, which sold for nearly $1000 20 years ago was a pretty good clone of the Blake Victory...the original W-C Skipper for about $750 20 years ago was a close clone of the Baby Blake...and adjusted for inflation, their prices today would be close to the price of the Baby Blake. However, both were discontinued when Thetford-Norcold bought W-C (the Skipper II is a poor plastic imitation)...W-C doesn't even offer parts for 'em any more.
These toilets are all bronze and designed to work differently from the common piston/cylinder toilet. Flush water intake and discharge are separate, for one thing.