Unkillable UEFI bootkit for Linux in the wild

ESET researchers: “Even though the current version from VirusTotal does not, at the moment, represent a real threat to the majority of Linux systems, it emphasizes the necessity of being prepared for potential future threats.”

Yeah! Get prepared by buying ESET Linux anti-virus, even though the majority of Linux systems don't need it, and getting this Bootkit installed involves getting root as a prerequisite.

How are bootkits "at least practically speaking, undetectable and unremovable"?