You can buy a used phone that will give no money to Google. I also hope for it to come to other smartphones, but not at the cost of compromised privacy and security. The reason that GrapheneOS only runs on Pixels is that they support the specific hardware requirements of GrapheneOS, including having an unlockable and relockable bootloader which is pretty cool of Google. I am sure that the GrapheneOS team would love to move on from being tied to a specific vendor's hardware and are working with Motorola to do just that.