In my mind, it mostly is about curl|bash not being auditable. On the spectrum of [auditable to not-auditable], curl|bash is as far to the right as possible, with things like distro packages far to the left. Maybe for a specific piece of software that's okay, but I think we would readily agree that it'd be a problem for all components of an OS to use bash|curl.

Bear in mind that, like many bits of security advice, this is highly context-dependent. It may vary based on your risk tolerance, your level of trust in the vendor, how robust other parts of your infrastructure (e.g. threat monitoring tools, network segmentation, etc.) are.