To ascribe good faith here to Zuckerberg is quite the leap considering his history. Why are his main products basically walled gardens then?

It is a business decision to open source his models, because he has been behind the curve from the start. Do you believe if he had chatGPT, he would open source/weight it? I don't think so, he would treat it like Instagram.

The point is, AI/LLMs are seen as the next frontier. If one of the closed ones becomes dominant, then that company can use its user base to attack Zuckerberg's platforms. That google failed with google+, does not mean the next competitor will.

A telling sign is how he integrated his AI into whatsapp. It seems out of place to me to have an LLM integrated into whatsapp, but he desperately wants a part of the AI cake.