This will keep happening so long as GrapheneOS is a "niche" operating system. We need to build up economic leverage by increasing GrapheneOS usage numbers until they can no longer afford to block it.
Isn't Motorola releasing phones with GrapheneOS next year? It should vastly increase the number of users.
An OS available either for one Google product line or for a phone costing over 1000€ from Motorola, will never reach usage numbers high enough to change corporate policy on business grounds. (It may happen some executive within the company is just sympathetic to libre software even where there are no business pressures, but that's a long shot.)
Anyone who has been around in the free-phone community in the last decade-plus would recognize such idealism as mistaken and never once borne out in practice.