I feel like it's mainly nostalgia/tradition for me. I reject the claim that those are bad reasons for keeping them in
I can respect that perspective even if I don't exactly agree: it's most likely the difference between your nostalgia and my more turbulent memories of it.
I've certainly met many people who very much fall into the category described. Your experience is not universal.
Oh, I understand that. I've helped countless people make characters over the years. From my perspective, alignment just doesn't "spark the imagination of people" the way it seems to for you. The tiny blurb in the book under alignment is dwarfed by character types the person has actually experience in book or film. and it's much easier to latch onto the idea. IMO it's far from a "very useful niche to have filled" that could be filled with actual advice on character building. I can honestly say, I don't recall anyone I played with read the alignment section and say 'oh NOW I have a good idea for a character'.
It usually does in context, and it's a lot quicker to write (often an order of magnitude quicker, since it's two letters and a good description will be at least 20), and that's a huge deal in published adventures and the like.
And remember, Paizo probably makes more money on published adventures than anything else. Things being good for published adventures is important for Pathfinder.
Oh I understand, but they also add alignment in for NPC's that are more fleshed out: they makes a 2-3 page detailed background and profile of an NPC in the back and you have to spend ANY space on alignment? Second, it's not as much space when it covers multiple creatures. Thirdly, if "a good description" takes so much space, I think it illustrates how little the alignment actually informes. You can have diametrically opposite outlooks easily fall under the same alignment.
Replacing alignment with a more complicated and comprehensive moral system with actual mechanical weight is totally a valid option. It is not, however, the same as simply removing it, and is in fact a much more in depth change to the game and how it functions.
Oh, I think you misunderstand. A moral system doesn't need to be more complicated and that isn't what i'm advocating. Quite the opposite actually. You wrap paladin/cleric codes into the gods tenets and they work for all followers. Simple, easy and everyone can agree with clearly spelled out do's and don't. IMO, much LESS complicated that trying to figure out 'is this x alignment' we have now.
Anything else falls into 'good' and 'bad': just drop law and chaos as they seem to have little impact as is.