There were no rationale and I'm not for or against it, it is jsut that a lot have been changed recelty from Québec to QC.

I would even remove these province tags since contrary to cities and municipalities for which borders are variable and may not be up to date, the delimitation of the province is more robust and more up to date (except for boundary with Labrador which is still not permanently defined). I created a tread on the OSM Canada forum: https://community.openstreetmap.org/t/addr-province-tags/138129