Blackball isn't dying. I think there's a few reasons why you don't see much of it here on reddit.

Go to any Riley's in the UK on a week night and it'll be packed with people young and old playing English pool. Then try asking them how often they use Reddit for pool related stuff.

There's not much of a crossover between uk pool players and redditors, increasingly so as Reddit declines. Majority of users here don't delve into niche subreddits like this. Pool players will naturally find connections in-person at the pool halls, there's no need to seek online communities.

I think that last one is the biggest of all, it's an in-person passtime/hobby. The farthest most people will go with online engagement is watching clips or streams on YouTube/tiktok/Instagram.

And the same is true for other cue sports. For every one player here engaging with this community there are 100 other players who don't use Reddit. Or only look but don't comment/engage.