This stuff was reported as bug by many players 
I think too, that it was design mistake. It was like this since Democracy 1.
EVERYTHING is capped between 0 and 1 - every simulation, situation, policy, their influences, event/dilemma requirements and effects.
Its using neural network.
Game eventually completely stabilizes over time - that is nothing changes anymore unless time simulation triggers situations.
Also higher amount of policies also stabilize game, as more stuff is pushed to 0 or 1.
Accumulators were suggested: On accumulators
Essentially have some things grow unbound.
Some things would be split between population, its growth, GDP, its growth, and GDP/capita.