TPI has or had some first rate posters and great discussions. The older threads there are a goldmine. You can go back over ten years and see good content. Sadly, it is not nearly as active as it once was.
There are a number of factors that have contributed to this.
First, you need to register to even read the forum. I can understand the logic of that in keeping trolls and net trash away, but it cuts down on potential membership.
Second, sadly everyone is going to social media. I really hate this. Minor rant time. It is much easier to find categories and topics in a forum, and to look over old threads. Good luck Try to find something that was written a day ago on facebook--forget about a week or a month ago.
Finally, their technical issues resulted in the forum being inaccessible for a while.