zlacker

Qualcomm offers the feature as an option to every OEM using Snapdragon. Our understanding is that it costs extra money to license, like many of their features including security features. Snapdragon is immensely expensive for a modern flagship SoC with long term support and the full feature set including security features.

OnePlus supported it on several devices but then removed it in updates fixing serious security vulnerabilities. Their non-stock verified boot support was insecure and instead of fixing it they removed it. It's likely there wasn't a clear or possible way to fix it due having a poor implementation which never worked properly. Fairphone 4 had a completely insecure implementation of verified boot trusting publicly available AOSP test keys. Having support for it really doesn't mean it works or will even keep appearing to work in future updates.

It's also just one feature. Our overall hardware security requirements are listed at https://grapheneos.org/faq#future-devices. People focus too much on relocking the device but we require a lot more than that. There are non-Pixel devices with essentially all the features we require such as the Samsung Galaxy S10+ and S10 Ultra but they don't allow using another OS without losing the security features. The updates are also still not what we expect, but if Samsung actually make it possible to support their devices we could accept some compromises. On the other hand, supporting far less secure devices missing things we consider hard requirements like memory tagging needed to provide our core feature set doesn't interest us.