The cause&effect actually seems to be reversed - it seems that relaxation of heavy-handedness is simply an early visible symptom that the regime is finally so weak that it's forced to accept compromises that it never had to.

The regimes would never ever accept them unless they were already close to toppling (Gorbachev times are actually a nice example, http://www.aei.org/issue/foreign-and-defense-policy/regional... is an okay description), since [appearance of] strength is required to keep them in power.