I've worked on those projects too. The most frequent reason is zoning. It's hard to rezone commercial into industrial and governments avoid it like the plague as it lowers property values. Other common reasons why is because the expected truck volume estimated for the distribution warehouse is unacceptable for major thoroughfares used for commuting. There's a lot of reasons actually, even security believe it or not. But like i said, it cost more to develop new land vs rehabilitating existing.