With respect to grapheneOS on samsung, I don't think it's about security. It's about openness, there is already samsung knox (or whatever it is called, samsung dex?) so clearly they know how to make a secure enclave it's just that samsung wants to keep their stuff proprietary.
In general samsung and others (huawei, etc.) are trying to get a grip on android, and open-source seems to oppose that.
I don't know what motivates google to lean in so hard with open-source ( maybe trying to prevent fragmentation or avoid future antitrust or set a "clean" example standard for stock android with their pixel brand ), but we do currently enjoy its fruits.
In general samsung and others (huawei, etc.) are trying to get a grip on android, and open-source seems to oppose that.
I don't know what motivates google to lean in so hard with open-source ( maybe trying to prevent fragmentation or avoid future antitrust or set a "clean" example standard for stock android with their pixel brand ), but we do currently enjoy its fruits.