Hi David… this was in the News a few days ago… and I remember making the same observation as you have… IMO that decision is just plain stupid.
The official reason the Haute Alpes gave for removing the 70kph was that they did not wish to over-restrict the drivers.
Regarding the new 90 sign on part of the route last night… this was mentioned in the News on a separate occasion. There are certain Departments, who are fully complying with the new directives, but they asked to include a “special” 90 sign on certain, short bits of road… where it could be judged to be “non-dangerous” and an aid to traffic flow.
I had read about it, but not visualized what they meant… it suddenly became clear last night.
You can’t miss the signage, on entering and leaving this special section… and it works…
The speedier folk zoomed past, overtaking everything in sight… fair enough.
Some cars returned to 80 as soon as the 80 sign re-appeared at the end of the “overtaking” stretch.
Some cars carried on at 90… some went on to 90+++ in spite of the 80 sign.