All dragons in 3e can speak, but very few can transform into humanoid creatures and only the oldest ones are very powerful spellcasters.
Sounds like your DMs have been running dragons in a fairly boring way, without any real personality for each of them. As for the hyper-intelligent and extremely wise, have you looked at the stats in the MM? There are lots of relatively dim dragons out there. It takes a white dragon to reach over a century in age (i.e. Adult age category) before it can even reach average human levels of Int and Wis.
So what's stopping you from making them so?
As noted above, there is a wide variance in powers, abilities, and intelligence amongst dragons, as you'll note if you take a look at the MM.
Because even the most powerful dragon can be taken down by a small group of the most powerful humanoids? And dragons take way longer than humans (for example) to become incredibly powerful.