Yes, but that's the beauty of gambling. The more you commit the bigger your loss if the winning ticket ends up being one of the 15000 you didn't buy.If someone mega rich really wanted this house they could just buy say 30000 tickets, at £750000, which means they will have more or less a 3/4 chance of winning and at a much reduced price if they were to actually buy it. Not to mention if there isn't a winner then you'd have the same chance of walking away with all your money back plus a few grand from other ticket purchases.
Even if you were rich would you be comfortable potentially writing off £750k? There are certainly other things you can invest that sort of money in with guaranteed returns.

Someone could create a nice paint balling club/business with that space.