Balance, for the most part. The classes with low skill points have significantly better class abilities than some others. Fighters have more feats, wizards and clerics have the most unrestricted and best spell lists. And when you think about it, there aren't all that many skills your classic warrior, wizard or priest needs beyond the few given to them.
Now, myself, I would like a general upping of skill points across the board because I like characters using lots of skills, and I'd probably drop the idea of class skills save in very special circumstances. I like the fighter that is also the eagle-eyed scout and who knows the local royalty and knows seven languages because he's been to ten different lands while he was in the army. Or the wizard who is also a good herbalist and woods-wise healer.