Embedded guys don't like command authentications, I think because it's an SPoF with probability attached that are repeatedly tried. They know bits flip and program counter skips, and so they even avoid use of "or equals to" conditions for loops. But they're using signature enforcement in cars nowadays, so that particular fear should be slowly subsidizing.
I would imagine the overriding reason people resist encryption is that it’s a pain in the ass.
You have to worry about long term key storage and security. You introduce a whole new class of failure mechanisms. It’s always going to lurk at the bottom of the todo list.
