Pre-orders are a business decision/necessity.
For a company the scale of Hot Toys, which does nowhere near the amount of sales as a standard retail toy company, they most likely have a lot less room to play around with their margins.
They sell less overall numbers and probably have a smaller profit margin percentage on each figure sold. Pre orders allow them to get a rough idea of how many figures to actually produce. If they blindly overproduce a ~$250 figure that doesn't sell as well as they hope, it could really hurt them financially.
The long lead times most likely have to do with the planning of their production. This isn't Hasbro or Mattel, who can create molds and mass produce dozens of individual toys lines simultaneously. At most, Hot Toys can probably only produce two or three figures at a time.