I can't believe they're at all worried about Linux on phones yet, not with the state mobile Linux is in at the moment. It's improving, but UX improvements on Linux tend to move at a glacial pace. I think desktop Linux has mostly caught up such that laptops can be sold to the general public and not be a complete disaster, but it's taken, what, three decades?
They might be concerned about future competition with a looming potential breakup of the company by the US DOJ (not that it would necessarily weaken Android itself but it seems plausible). But it could also just be because one of the devs wanted to do it, which is pretty typical with Google (for better and for worse).