Of course, that's probably got to do with bus factor. A similar story happened w Paranoid Android, only OnePlus hired several of their devs to work on OxygenOS, and the project hasn't been the same since.
For MIT, BSD, Apache 2, it's quite easy for a company to hire a handful of active maintainers and starve the original project by redirecting their attention to a closed-source fork. http://hintjens.com/blog:27
GPL, and especially AGPL, are better in this regard.
Second, LineageOS might not ship Google apps by default, but opengapps makes it possible to install them, and Lineage OS installation guides mention it as an option. I guess many people do it so that they can participate in the Google ecosystem. So Lineage OS only adds more customers to Google's apps and services, more eyeballs that Google can sell.
The main damage is dealt on the device vendors due to the LineageOS use case as an aftermarket firmware creating less need for people to buy their new hardware. My phone was released in 2014. I bought it in 2020 and thanks to Lineage OS, I can use modern Android on it. IMO since then, phones have gotten worse in many regards (non-removable batteries, no jack, glass everywhere so that phones break more easily, overall more expensive, etc, ...), so I'm quite happy with this setup.