It's not dead yet...
The issue with the forums is that a limited amount of online activity gets spread around: some only join the official clubs, some don't join any at all, some only post on facebook/instagram/snapchat/tinder and such, and some go completely mad with new forums breaking out of old forums, forum takeovers, and the social/performance/modification/track gangs all heading their own seperate ways and being rude to each other.
I suspect however that most 991s are still in warranty, don't go wrong (or if they do, it's back to the dealer), don't "need" new tyres or brake pads or suspension parts, and the owners don't actually need the knowledge and information from the forums. And they have enough mates already.
The rest of us, we're online for the banter, and the advice, and the community. And the not-stock cars...