We don't know all the factors that contribute to Olympus fate and certainly there are many of them - but purely for the sake of argument pointing out that Olympus does something which Canon doesn't can't really be used as an argument for Canon to start doing it anymore.
I would also like to see an option for AS grooves on the collars, but the only long lens I own with a foot to begin with is my Sigma 150-600 mm C - which also does not have the grooves.
A few others things to think about:
My AS plates are getting some signs of wear from use with all the heavy equipment and some too hasty assemblies. I do prefer the optional attachment to wear down, rather than the first party accessory.
When brands like Sigma or Canon put a collar and foot in a lens, it likely weights more than a Olympus design with this feature. So the requirements for the manufacturing may be higher.
AS is not an official spec (
source) , it is just a rough dimension many accessories producers roughly target with their plates and clamps. But I don't think there even is an option to license it, so the height of this royalty isn't a factor. I rather believe Canon is not a fan of reverse engineering a spec that is not official and would prefer not to get in trouble if it turned out that their interpretation of the spec didn't match the one of some clamp manufacturer and gear was damaged due to incompatibility.
This lack of an official spec and license may also factor into considerations for marketing and legal documents. This could well contain aspects of Japanese law and copyright that we have no idea of, but Canon understands very well and believes the value added to certain customers is just not worth their perceived downsides.