Nope, your imagination is not overactive, or at least not completely so. I've worn many a pad in my time - diapers work better, but pads work fairly well, if they're not the ultra thin type. No pad made will take a full pissing, but they will take a lot of slow dribbles, or quite a bit of urge overflow situations. I can't speak for others, but for me, the femininity of the pads only adds to the sexual excitement. Also, pads are easier to hide, both before and after using. I've recently found that they work fairly well as booster pads as well, while keeping the bulk more manageable. I have to keep my wearing fairly well concealed, so maintaining the balance between bulk and visibility is high on my list. Over time, I've perfected ways to hide pads that would make most women jealous - even my SO, who knows I wear them at times, can't tell when I am.
Now, to directly address your questions:
Q - They absorb (almost) nothing, so why wear them if you don't have to?
A - For me, at least, absorbency isn't as important as just wearing it.
Q - Maxipads might work if you only want the feel of bulk cotton/plastic without actually wetting or messing because maxis are cheaper, more discreet and more readily available, and are a symbol of feminity. Since they don't absorb, is there another reason for a pad/tampon fetish?
A - They do absorb, and some of them a lot more than you might expect, but that's not the point here. Another reason? I really don't know - I find the same fulfillment of my needs from a pad or a diaper, but that's just me. Perhaps the sexual nature of pads makes them more attractive? Or maybe the "taboo-ness" of them, since their use by women is so hidden and hush-hush?
Hope that helps!