Looking back on my many, many years of eating in restaurants (which I do way more than I should), I honestly cannot remember a single instance of sub-par service. Don't get me wrong, I'm sure I've occasionally experienced what you would classify as poor service...I just don't remember any examples.
How can this be, you ask? It's easy: I just don't care. Seriously, if I have to ask for a water refill three times, who cares? It's not like I'm going to exceed my "Can I have more water?"-asking quota, and asking is certainly not going to shame or emasculate me. Besides, maybe the server is in the weeds, and just forgot. Whatever the case, you know what usually happens when I ask for a water refill that third time? The waiter & I have a friendly laugh about it (usually he says something along the lines of "it's one of those days" or "it's been so crazy, I need a drink", and I say "I hear ya man, it's a madhouse in here tonight"). You know what happens next? I end up getting friendly, extra-attentive service, feeling great about my experience, and leaving a better-than-average tip.
On the other hand, a friend of mine used to ask me for restaurant recommendations (I use the past tense, because I stopped giving him recs for reasons I'm about to explain), and, without fail, he would come back to me with complaints about the service. After dining out with him a few times, I know exactly why: he doesn't say "please" when he orders or "thank you" when something is brought out or refilled, he doesn't chat/banter with FoH staff, and when there are service or kitchen snafus, he comes off as aggressive & upset. Meanwhile, his wife (who has very legitimate medically-necessary dietary restrictions) asks questions about items' ingredients without even a hint of a smile, in a way that is a blend of all-business and a kindergarten teacher asking a student if he forgot to close the lid on the class hamster's cage (knowing full well that he is guilty). You've seen the type: "Is this item vegan?" "Yes, I can assure you for a fact that it is vegan." "Okay, but does it have any animal products in it?" "No, it does not. It's vegan." "Okay, so it has no meat or dairy of any kind in it?" "<sigh>...that's correct...<eye roll>." Between the two of them, it's no wonder they experience poor service so frequently & consistently.
Let me ask you: when was the last time you went to a restaurant, and genuinely asked your server how her day's been going? Or which item served there is her favorite? Or, when she forgets your sauce on the side, asked her for it in a polite & friendly manner, then laughed about it with her & offered some empathy for the rough double-shift she's working that day? Truly stellar service (as opposed to just "good" or "acceptable" service) doesn't just magically happen - it almost always depends on the customer understanding that the server is an actual human, not a mindless automaton or TV butler.
So to answer your question, "why do foodies forget/neglect service?" I don't...like all injustices in life, rather than letting a bad experience ruin my good time, on the very, very rare occasion when my server is less than friendly, I let it go...after all, next time I could be seated in a different, friendlier server's section. Plus, life's too short to let one apathetic server ruin my evening out. In most cases, however, I don't get bad service because I try to go into the dining experience with a positive, friendly disposition. Because, as Sir Paul said, "in the end, the love you take / is equal to the love you make"