The same reason most communities are dead; lack of new blood.
Communities always lose members over time, and new people need to come in to replace them. Tulpas just haven't garnered any attention the last few years, leaving the community to rot away.
>Anything we could do to "promote" this place or something like that? tulpas are one of the coolest things ever i feel sad seeing the lack of interest.
I don't think there's much we can do about it.
Tulpamancy caught on initially because it was a new thing. A little bit of visibility was all that was needed. But now it's just one of the many weird things that you can find on the internet.
The other issue is that the boards don't really serve a purpose beyond trying to convince other people to get into tulpamancy.
If I recall correctly, the most alive threads were FAQ/Help threads, followed by "please post something so the board isn't dead" threads.
Topics such as progress, what is your tulpa like, what is a cool thing you did with your tulpa or the tulpa talk shitpost thread didn't go anywhere, nor do they facilitate any long-lasting discussion.
I think that if /tulpamancers/ wants to go anywhere, it should actually serve a purpose.
Given the imaginative nature of tulpamancy, exploring ideas together and trying to provide inspiration for one another might be a decent direction.
Maybe art threads, but I feel that anyone half-decent might avoid it as to not get any association with the tulpa community. I know I would.