I've often wondered, as I look at IC datasheets and do PCB layouts, why don't manufacturers keep related pins together?
Example: 74HC597 and CD4021 parallel/serial interface ICs are both 16-pin DIPs with 8 ins or outs. Yet, invariably, they're not sequential. You'll have I/O #2 and #3 on different sides of the chip for instance. I'm sure current fabrication is just following suit with legacy parts, but somewhere in a lab long ago, an engineer decided to randomize the pinout.
Op-amps OTOH generally have a very sane layout, like the TL074 for instance. The +, -, and out pins are in order, and those groups are mirrored on each corner of the IC. (Although, the V+ and V- pins are on opposite sides of the TL072 and TL071 variants, which almost cost me two chips from my own carelessness. So maybe it's a universal sadism?)
Is there a good reason (breaking up coupling for instance) or just an engineer trying to impress upon the world the same manner of chaos as might be found at his work area?