Orrens, I asked this question on TD a few years ago.
My curiosity was aroused because there seems to be a lot around and nobody seemed interested in harvesting them.
This sort:
https://teakdoor.com/images/imported/..._small_0-1.jpg
I did some research and found that France imports them at a very good price, so even if the locals don't eat them, there's still a market.
As far as I know, Thais won't eat land snails. I don't know why. Perhaps it's a hangover from the days before indoor toilets and the fact that these snails only eat rotting vegetation. Rotting vegetation may be associated with outdoor toiletting? Whatever, it is strange, as you say, that these snails aren't on the menu in Thailand.