Why don't AI in fighting games ever do combos?

Dependes on the game.
Many FG, the AI make combos.

while it is possible, I think another aspect that maybe they have difficulty judging is the distance. We know from experience that if we are x pixels away then a specific link works. We usually account for this by performing setups to get us in position to do the link. What setups to the AI have? If not done right then it could end very poorly where you bait a missed link and counter then while they’re recovering from their link attempt. I’m sure to some degree they can tell distance (different normals depending on distance from opponent). But is that really something that we want the CPU to be processing throughout the match?

SFEX3 Shin Bison had hardcoded combos which he exploited every time you were open. And when most of the combos deal 50-80% damage, and he had infinite super and he took less damage than the rest of the cast. All it did was create a situation where people well at least I would just turtle the entire match only countering known moves that are unsafe, and kept all of my counters and combos safe from his counters and combos. He can literally punish a blocked fireball from midscreen without any effort. Hell a landed fireball he can still punish from midscreen.

But those are combo heavy fighters where as Most Street Fighter games aren’t.

I sure don’t want the AI to do 30 second long combos on me when I play against the AI…