The two most controversial terms of the concordant were the banning of the worship of Talos and the cession of a large section of southern Hammerfell (most of what was already occupied by Aldmeri forces).
If you go up the stairs in Understone Keep, before Jarl Igmund of Markarth's throne, and stand around the Thalmor Wizard or Soldiers for a while, eventually they'll just say "Worship of Talos is strictly forbidden" over and over so you never forget that the Thalmor prohibit worship of Talos.
The Thalmor seem to have significant clout with the Jarl, hence why they hang around his Keep all the time, and both the Nords/Imperials and the Thalmor are fervently against deviance or worship of false gods like Talos.
Given all this, why does Markarth's Shrine of Talos yet stand, and continue to operate, and allow people to pray there? Why haven't the Thalmor or other Talos revisionists firebombed or shuttered it?