- If you want a non-bloated, mostly-AOSP ROM with updates for many years, installing LineageOS (or another third-party ROM) used to be the only option; whereas these days, the Pixel phones give you most of this, and you can just buy these in a store instead of needing to manually flash a ROM.
- The stock ROMs from most manufacturers are less horrible than they used to be. I'm not saying that they're great now, but there's a pretty huge difference between most new phones today and a KitKat-era cheap Samsung phone.
- As you said, I suspect that GrapheneOS has supplanted LineageOS for many of the enthusiast users.