Grapheneos has well established its role in the android ecosystem. Having developed and upstreamed features that have as a whole, improved the security of android.

Pine64 has targeted a very different market around extensibility and hacker/maker mindset. However while their phones have a lot of potential, security measures are half baked (microphone cutoff switch doesn't actually cut off the microphone), performance mediocre, and demand missing. While I love my pinephone pro, its not a dailiable device. A phone that cannot access common services like your bank account are non viable for 99% of users.

Plain Linux on phones is still quite bad. It's not unusable like it was a few years ago, but it's still not good enough to gain any traction. Jolla is trying, desperately, and it's not working, even with the ever growing anti-American sentiments.

For Motorola to partner with one of the Linux phone projects, someone would have to invest significant resources in mainlining the drivers, replacing blobs with open source drivers where feasible, and maintaining that code when new upstream firmware and drivers make it downstream with patches and fixes. Looking at postmarketOS, you can see it takes years of community effort to port a device to the point of becoming useful. Once the software is done, the hardware is outdated enough that Motorola won't be making any money on sales any more.

In theory all of this would be a lot easier if Qualcomm, MediaTek, and the other SoC manufacturers would take the burden of mainlining drivers upon themselves the way Intel and AMD do. With the recent high-end Qualcomm chips, the company does seem to put in some effort, but these companies simply don't care about Linux support.

GrapheneOS is an Android fork so of course they're partnering with an Android company. They also don't have the capacity to maintain their own kernel + security patches + drivers, which is why they rely on upstream maintenance (from Google, historically) with their own Android-level improvements to remain secure.

Because, and I really mean no offense to them, their phones fucking suck. Like, dogshit slow hardware with terrible drivers and a modem that barely works with last gen tech.

Their most advanced phone is based on a >10 year old SoC, that wasn't even that good when it was first released.

Apps. Any phone without access to the Android or iOS ecosystem is doomed to fail.

The only solution would be an emulation layer.