the reason they are selling is because they want to profit from it.
some people buy blocks there for investment only, with the purpose of selling them in the future for a profit.
our block of 667sqm 2 yrs ago costs around $165K. now, with that size, blocks are selling at $250K+. and it depends on the location within Pt Cook. if it's near the freeway and shopping centre (currently being built), blocks 600+ sqm would be more expensive.