This project is suspicious

Where do they say others can't use & contribute to GPL3 projects? Nowhere that I can see. Nor are they saying those that use their project CANNOT use or contribute to GPL3 software. However, they are saying that some organizations don't want to use software licensed under those terms, so they are providing software licensed other other F/LOSS licenses (https://github.com/uutils/coreutils/blob/main/LICENSE for coreutils). It's not my favorite (which is GPL2), but it's F/LOSS, same as BSD. I personally won't disparage people for using a BSD OS instead of linux. It's still F/LOSS.

>they say it's for regulatory compliance, then it's difficult to also claim that they have no opinion on whether it's really necessary for said regulatory compliance.

No, they claim their customers say its for regulatory compliance. See mwelchuk's comment on that.