well, because you have to pay the price of turning into an umber hulk, which isn't a popular creature among any people (and even more so if any of the locals would witness your shapechanging). So to speak i didn't shift into any dragon form, so those forms are also without -real- true seeing?
All in all i would rather see some -price- (i.e. components) added to what others could perceive as powerful or unbalanced (i hate this word) instead of making many spells much different to what they were originally in game (otherwise there are many things that should be revamped as well - rolling hit points on level up with out rerolls, making stealth system properly, proper trip rules, speed movement etc.) or even in some cases to what they should be per book description (i.e. animating and creating spells), but thats some other topic.
So all in all there is no -true seeing- as it was designed by developers at all?
(as for stealth, i heard about someone having ms and hide close to 70s, soooo.... how to counter that in game uhm?
) +20 from spells won;t help much