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.
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. I think ROMs such as these also explicitly mention that the bootloader cannot be locked once said ROM is installed. I understand if someone doesn’t have the time but if they had enough time to understand how to flash a ROM on their mobile one would think they’d be interested in such details too (well, if they aren’t, then they likely don’t care).