Some build combinations make completely useless images. For example, an "AWS ISO" is, by itself, a completely useless thing because a) you cannot deploy an EC2 instance from an ISO image b) using such an image on any other platform makes no sense, and worse, it comes with a cloud-init setup that essentially becomes a backdoor in a non-isolated network because it blindly trusts config data coming from a certain link-local address.
We should likely disallow booting such flavours from a live CD. We already have live CD detection code in our save script. We can add a --allow-cd-boot build option that would add that check to boot or install script and make the image refuse to work and show a prominent warning to the user.