two said:
A paralyzed wizard standing in combat generates no AOO's for being paralyzed.
A paralyzed wizard standing in combat who casts a stilled, silent spell generates an AOO for casting a spell in combat.
In both cases the wizard has stopped moving and "people in combat no longer consider them a threat and so don't flail at them and so there are no random attacks the paralized character can accidentally get in the way of".
But one of them generates an AOO, and the other does not.
Then you don't have a problem with AoO's, but with some specific situations that don't make sense for you.
Just make a house rule: a spellcaster that casts a spell with no somatic, material, focus and verbal components while paralysed does not provoke AoO's.
Does that make sense? Yes.
Is that balanced? I think so.
Does the PHB need to waste its space with such a specific ruling? No. That's up for the DM's to adjust their games.
AoO is a very metagame and abstract rule, and rules like that such as AC and HP don't make any sense in some very specific situations with we try to deeply rationalize them. You can create mini house rules to address all these little inconsistencies in order to fell better about them, but the way they are doesn't break the game, it just looks odd.
But by doing that, you can very easily break the game, or create even more absurd or unbeliavable situations.
If instead a character must make a concentration check in order to drink a potion, suddenly wizards and sorcerers become the masters of melee-potion-drinking.
If instead characters get flat-footed, barbarians with uncanny dodge can do whatever they want in combat.
Being paralyzed in combat = stupid situation = get hit with AOO.
From the metagame bunker, that's false.
Bad choices should be penalyzed, and you don't choose to be paralyzed.