I think the industry/market generally realises that Graphene is the most secure Android OS there is. I’m interested in trying to understand how they implemented locking the bootloader and why other ROMs aren’t picking this up yet. Maybe it’s just a lot of work.

From what I know it isn’t only about “a lot of work” its about phone vendors having to support that in the first place.

I think people who go on to flash Calyx definitely know the advantages of locking one’s bootloader and that using Calyx doesn’t let you do that

From what I see in this post and others doesn’t seem like it. Seems like a lot of people are unaware of this issue.