I think it comes down to first and foremost scratching one's own itch in things. Most are just creating/updating things they need. This can be a company's contribution (AMD/Intel) to support their products, or it can be an individual fixing a bug or implementing a needed feature. It can also be company devs contributing to something that is adjacent to their own needs.
Where the FAANGs/Clouds leach a bit is when they offer a service monetizing what the creator of that service/software is using to monetize themselves. Can they do it, sure... should they, maybe not. I think, for example AWS could have made an offer for a more limited licensing agreement to Elastic, offered direct funding, or developer support, or buying them outright. Instead they forked, offer their own SaaS for the product, and carry on. Leaving Elastic to develop/support the core product.
Where the FAANGs/Clouds leach a bit is when they offer a service monetizing what the creator of that service/software is using to monetize themselves. Can they do it, sure... should they, maybe not. I think, for example AWS could have made an offer for a more limited licensing agreement to Elastic, offered direct funding, or developer support, or buying them outright. Instead they forked, offer their own SaaS for the product, and carry on. Leaving Elastic to develop/support the core product.