Unless you're playing on Hard, this is incorrect. Lucky nations get 25% less AE but for the most part the reason AI doesn't get coalitions is because it paces itself when expanding.
The problem with this is that it is a positive feedback loop.
They get less AE, so their pacing is less threatening.
Because they tend to pace slower, they get even less AE.
Because of both of those, they can expand and expand and expand without ever facing the consequences.
The settings they get fuel growth which feeds back into being able to easily further grow.
It's why France, without player intervention, simply grows and grows and grows apart from the rare 1 in a 1000 game where they suffer an early defeat by combined Burgundy/Castile/Whoever alliances.
Don't you think players get tired of being forced to manage France in every campaign? Just once I would like to see Burgundy, Castile, Aragon, England become the superpower threat in the west...
A player by contrast much manage AE every step along the way. Hell, you can get a coalition from a single province at game start.