The suggestion of switching to a forum seems to come up twice a year for years now.
Some people have even done so, but people vote with their feet, so to speak. Running those forums costs time and money, and no-one's stepped forward to foot the bills for that. And my experience with forums is that the active community size is always about the same as with a mailing list--a couple dozen people account for 90% of the posts.
There will never be a thriving LD forum until the LD mailing list is turned off by the owner.