Because it pretnds to try to be deep. It's like a 12 year old geek using big words trying to sound smart or deep when they really don't udnerstand it. KOTOR2's 'deepness' comes off as fake; not wise. Kreia is the biggest tool for this.
Her constant splattering of her 'wisdoms' is away for her (and, the devs) to yell out," Look at me! I'm being very philosophical! I am THA smrt!" I literlaly roll my eyes at her.
Play PST, and KOTOR1 for examples of 'wise old characters' who actually come off as wise instead of 12 year old wannabes.
KOTOR2's story is not deep. It's not shallow either comapred to most games. It's just there. Just like KOTOR1.
Both games are fun with intersting character, stories, and quests (for the most part); but are not deep for the moost part. The series, as a whole, are way overrated.