I first joined Lemmy back during the big Reddit exodus of last year. I like many others wanted an alternative to Reddit, and I thought that this might've been the one. I made two accounts, one on lemmy.world and another on sh.itjust.works, in the June of last year that I used on and off for about 4 months.
At first Lemmy was exciting because it was so active. There were so many new users who were enthusiastic about turning this platform into a genuine alternative. There was a communal effort to create and interact with content, and for awhile it worked. Lemmy was truly interesting during the summer of last year. However, this stream of dedicated users started to slowly decline.
A lot of people hoped that if they were active, they would attract and retain more users to this place to the point where the community would foster interest specific communities like Reddit, but that never happened. After a few months, a lot of users lost interest and went back to Reddit where the userbase is so massive that there is an active community for just about anything.
With this reverse exodus back to Reddit, Lemmy ended up with the same groups that were active on it before hand: political extremists, tech nerds, privacy enthusiasts, and shitposters. To be fair, all these groups are larger now than they were a year ago, but that's all this platform has to offer. If you're into any of these things and primarly these things then Lemmy can be a good alternative to Reddit, but for the general masses? Lemmy is just not good.
For example, a NBA post on the NBA subreddit can get you thousands of interactions in a couple of hours. An NBA post on here will maybe get you a dozen over the course of a couple of days. The only content that will gain any traction here are tech news, political propaganda, and maybe some memes. I don't see this changing any time soon. Even if Reddit implodes, I still think Lemmy will remain a niche platform. I think this evident by the fact that this platform hasn't really progressed in a year.
Studies find that the vast majority of users on a platform are passive participants, the vast majority only look, a smaller group looks and comments and finally an even smaller group looks, comment and post. The key to growing any community is to find or be an active poster. It's also an investment, if you post and get only 1 to 2 reactions, that's okay, it takes time. It also means that more people see it and didn't react.
In your example the NBA sub, I am on it and comment from time to time, but don't have the sources or time to post, but if someone took, at least, the links from reddit and posted them here, it's a start. I know NBA reddit has a lot of good discussions which you can't replicate here without more people, but the posting of articles and links is a start.