It's telling that the 3.x developers were somehow terrified of a class that got multiple attacks per round and could actually hit with them on a regular basis, then they turned right around and gave monsters multiple attacks at their highest base attack, lol.
I never had a chance to hear a developer explain it, but my personal theory had to do with the Medium BAB classes, most of whom were intended to use weapons from time to time. If you make enemies purely with the attack bonuses of say, Fighters in mind, then pretty quickly Clerics, Bards, Rogues, and Monks aren't going to hit anything without massive buffs.
OTOH, if everything's AC is set to where they think a Rogue should be, you got Fighters just using Power Attack and Combat Expertise on every attack for "free"...or just pretty much always hitting.
Descending attack bonuses in theory prevent that sort of thing, I suppose. It's still clunky and inelegant and turning the game into "everyone stands still and full attacks, and monsters do more damage with their full attack than most players" is something I can never forgive them, as much as I liked the "build a character out of LEGOS" aspect of 3.x.
Then Paizo decided not only to not fix it, but give Fighters more built-in bonuses to hit so that you had level 5 characters with +12 to hit running around, lol.