The sleepy town that they grew up in and love.

The Mom & Pop coffee shop and hardware store.

The ability for their children to live down the street, because they have been priced out of the market.

There are many things that change when your house and land are worth more money.

Roseburg, Oregon/Douglas County wouldn't even cough up the money to fund their library system. Some places are not very, uh, forward thinking.

For some people their house and land aren't a crop to raise and sell, maybe they like their hidden gem for what it already is. See the lamentations on Austin's growing pains in this thread.