the problem/lucky-situation is that android without google (lineage os or graphene for example) is not that bad, its a pleasure to use and its good at privacy and decent at security (android itself its pretty secure, the smartphone is an insecure device by nature and backdoors still "under the android stack"). So, a lot of FOSS development still focus on android (fdroid is full of fantastic foss softwares) and not so many feel the necessity of mainline-linux-phones, so the development is not that heavy.

I think we have more chance to have a "better android" (based on mainline linux for example) than to have a good linux phone ecosistem not android-based, but who knows...