Or more specifically, why they don't all have magic items to match their ECL. It would be well within their power to acquire such items, and to their immediate and absolute benefit.
They could, but from a metagame perspective, this is problematic in that when the PCs overcome them, you risk the party getting much more gear than recommended for their wealth guidelines. It is more practical to give a monster extra HD than a +5 weapon and an amulet of con+6.
The crs in the books assume the monsters come as statted (ie: practically naked). If you give them additional gear, then you may need to increase their cr to reflect that they are now more challenging.
It would still be plausible for them to have 1 or 2 cheap magic items (MIC rocks in this aspect - I use it quite extensively to round out my monster npcs' capabilities), but unlikely that they be decked out from head to toe in magic gear.
On a similar but more off topic note, why wouldn't all dragons take 20 levels of a class as soon as they could? Instead of waiting 1000 years to reach the peaks of their power, they just take 20 levels of a class as wyrmlings and reach the same level of power in 5 years.
As a child, I doubt they will have the mental faculties to contemplate taking class lvs. I suppose you could rationalise it that they are confident with their physical prowess, and so do not see the need to improve themselves further by taking class lvs (which means extra work).
From a gameplay perspective, I think it would be cooler to pit your PCs against a fully grown dragon rather than a very young dragon with 20 class lvs.
You could do this. I found the concept horrific. By the time they whittle them down, youre not even playing the same creature.
I agree. I play a powerful race because I want the full package and everything which comes with the stat block in the MM, not some base race which simply shares the same name but none of its abilities.
If I play a minotaur PC for instance, I want it all - the stat bonuses, NA bonus etc, not a half-orc with horns taped to my forehead.