Property values have risen and people that own the properties are now looking to upgrade and make the changes. A lot of the old places are going away.
All you have to do is look around the area of sala daeng and you can see it.
Personally I think PAT PONG is going to be gone in 10 years if not sooner.
People are not interested in the market there and the stalls and the ping pong shoes are over done.
Every other part of the area is upgraded and from what I am told the rents that are being charged are through the roof.
Khao san had to make a few changes to stay relevant as there are not as many backpackers as there used to be.
For the rest of the city it is easy to explain Bangkok is a major international city therefore like Toronto and Ottawa in Canada and Las Vegas and other NYC and other cities it has to grow.