On many modern motherboards there is a backup bios that you can boot into by shorting certain pins. This can be done in about 10-15 minutes by a person with a metal paperclip, some basic technical knowledge and instructions from a YouTube video. I don't think there is even a mechanism to update this backup version, it's just a "known good" bios shipped with the hardware so that a bad bios update does not brick the device.
So even if they push an update, people can pretty easily downgrade to a vulnerable version if they want to.
I doubt there are actually many boards with dual bios. For a while Gigabyte had a lot of them, but for many years very many of their boards dont have this feature
So even if they push an update, people can pretty easily downgrade to a vulnerable version if they want to.