In the Java world, most major open source projects are sponsored by companies. Someone(s) is getting paid to maintain and evolve that thing as part of their job. Companies might do this to drive traffic toward the commercial "enterprise" version, for which they charge money. More commonly though, it's just something that they use internally... and they open it up for marketing/prestige/recruitment purposes.

In most other language ecosystems, most open source projects tend to be driven by individuals as unpaid side projects. That's great in a certain sense, and a large part of the reason why Java is less "cool" among young people who are eager to plant their own flag on an open source thing. But sadly, it's just really difficult to keep a major side project alive and healthy over the long-term without sponsorship. So those ecosystems tend to be chaotic and flaky.