I don't think that's the case, it's not philanthropy, they are getting something out of it. The labs are learning from one another from the shared models.
Plus I am certain it makes financial sense. I am guessing here but fully utilizing a subscriptions limits probably costs the operator more money than the subscription revenue, that is why anthropic is making such a big stink about the chinese data harvesting. By releasing the weights, you are relieving yourself from that burden because the competition does not need to hammer your subscription service they can just download your model and analyze it and run it all day.
Also for the largest models it makes no sense to run it yourself unless you are a major player. Renting the hardware is ludicrously more expensive than their subscription tens of thousands of dollars. And buying the hardware to run them is in the hundreds of thousands of dollars.
The primary benefit of releasing weights is the attention it generates. Some people have the hardware to run it, try it out because it's free, tell everyone about it, and then even people who don't have the hardware might get interested and pay the original developer. So it's a marketing expense, basically.
The most popular LLM product in China is Bytedance's Doubao. You probably haven't heard of them since they never released weights and don't benchmark particularly well, but Bytedance already had enough users on its other apps that they could directly advertise Doubao to.
I believe we are still very very early in AI development, so it doesnt even make sense to close models.
Open source and open weights model is how you can harness the potential of all humans to continue development and improving the SOTA of your model. Literally every student on the planet wants to play and improve these models for their own use case.
Plus the ecosystem, once you have users in the ecosystem on your open weight model, this is a giant leverage point in itself
That's not meaningfully different from philanthropy. If Chinese AI products generate sufficient revenue with cheaper marketing strategies, then the incentives for releasing open models will go away.
Right now, there is a shortage of talented researchers, and the attention that open models generate allow them to attract good hires. But this is a fragile dynamic that can break in the future. It's not very different from commercial open source work, except it's much more capital intensive and lower volume.