Dude, the answer is literally on the corresponding wikipedia page.

GrapheneOS currently is only compatible with Google Pixel devices,[23] due to specific requirements that GrapheneOS has for adding support for a new device, including an unlockable bootloader and proper implementation of verified boot.[24][25] In October 2025, GrapheneOS said that it was working with a "major" Android OEM on future devices that would support the OS on Qualcomm Snapdragon platforms,[26][27] and that they will be the flagship devices, expected to appear in Q4 2026 or Q1 2027.

I know it's counter-intuitive but there are very good reasons, which are listed on their website:

https://grapheneos.org/faq#future-devices

Short version is that Google prioritizes software development and (more importantly) security in their hardware above some other qualities.

Only device meeting the requirements. One of the only devices which allows relocking the bootloader. So it is a matter of no other alternative existing