Motorola has effectively lost in the Android market and are on downward spiral into irrelevance (already there?), so they have to do something different.
My friend the GrapheneOS supported devices list is nothing but pixels, including the very latest models. It'll be good to have more supported devices.
The question for Motorola is: "given the cost of meeting GrapheneOS' requirements, how many more devices will we sell?". Hundreds of thousands of devices is not nothing, I guess. Plus they get free consulting from the team building the most secure phone OS out there.
I really don't understand why smaller smartphone manufacturers didn't fight before for that. Say Fairphone: I don't know about today, but a few years ago they finally got profitable by selling something like 200 thousands units a year. If they had designed a phone to be supported by GrapheneOS, that would surely have increased their sales quite a bit. Now that ship has sailed, GrapheneOS will be focused on Motorola for a few years.