There's an old Joel Spolsky post that's evergreen about this strategy -- "commoditize your complement" [1]. I think it's done for the same reason Meta has made llama reasonably open -- making it open ensures that a proprietary monopoly over AI doesn't threaten your business model, which is noteworthy when your business model might include aggregating tons of UGC and monetizing engagement over it. True, you may not be able to run the only "walled garden" around it anymore, but at least someone else can't raid your walled garden to make a new one that you can't resell anymore. That's the simplest strategic rationale I could give for it, but I can imagine deeper layers going beyond that.

https://www.joelonsoftware.com/2002/06/12/strategy-letter-v/

What is the long game for tencent?

Maybe it was unclear, but that's what I'm asking too.