Not sure what the reasons are but I feel quite uncomfortable as a new user in this community.
It's literally not possible to just post anything but instead a "grace" period of 40 minutes between every(!) post is configured in this forum. There is also no way to edit a previous post to add more text afterwards to (at least) overcome this awkward limit.
But by the looks of it even then no post/topic is published and a manual(!) mod/censor needs to allow every written word.
I personally never came across such an UNWELCOMING environment and I'm quite disappointed that such drastic measurements are taken and manifested.
The obvious would be that the admins had problems in the past with auto registrations/spam etc. and made the decision to make it almost impossible to participate. (Spammer can now only send 1 spam post every 40 minutes instead of 40 posts every second -> mission achieved)
I don't know when and what happened but you should definitely check if it would be possible to have sane/human levels of restrictions that still allows interacting so that new users feel welcome and want to stay and participate in the community.
For me it might be already to late and the bad (first) impression (also about the for me personal weird/antique/bad to use forum software) will stick.
Any way I wanted to get this of my chest as probably none of the users who sign up and just leave annoyed are telling you this. (But you might get an idea when filtering for users with only 1 post for example).