I do have a certain "coldness of affect," which bothers me, though looking around me I'm not sure most other people are particularly affectionate either. Still, I never was content to be just average, and I don't see much wrong with aiming a little higher. There's probably a variety of reasons why I fall short of my own aspirations here.
I keep my mind almost perpetually busy with anything fascinating I can find, because it's the only thing that distracts me from my sensory issues, which drive me up the wall otherwise. If anybody says affectionate things to me, they're usually too sudden for me to tear my sticky brain away from what I'm thinking about in time for me to make an appropriate response. I tend to feel guilty because I feel I must be coming over as cold-hearted. I often manage some kind of compromise but my response can still be rather stiff and stilted because it annoys me to be interrupted. Of course none of this is their fault, everybody's entitled to a few affectionate words from those who profess to be their friends.
I'm also pathologically honest, especially with loved ones, who (to my mind) are particularly entitled to the truth from me, and I tend to feel that NTs fake a lot of the affectionate things they say - I hate doing that. I think it was Kingsley Amis who said in a poem that he found it hard to think of anything to say that was both kind and true.
I do say a lot of true and reassuring things, but they're often of a somewhat practical nature, and I tend to phrase them and intonate them in a not-too-sloppy way, which may suggest an expectation that the recipient should ultimately get a grip and stand on their own feet. I do get rather fed up of reassuring people on (what I see as) the blindingly obvious, such as "you've done very well," or "I care about you."
Anyway, for the time being people are just going to have to deal with me as I am, and just have a bit of faith in the affection with which I hold them. It's all there in my behaviour somewhere, I'm there for my loved ones when they need me, if they just have the guts to signal their needs reasonably clearly. At the end of the day I don't let them down. Occasionally I'll sense that I've not quite responded as well as they'd have liked, and I have this knack of putting my hand on their shoulder for a second or two. Somebody did that for me once when the boot was on the other foot, and it really helped, so with a little luck it's a strong and valid gesture that speaks louder than a bucketful of cliche-ridden, vacuous half-truths.
Interestingly, when I was living among a group of very warm hippies and anarchists, I was a lot more free with my affectionate remarks, I guess it was because I felt I was in the right environment to do that, and I don't think I came over as lacking in affection at all. "Straight" society is often a colder and more competitive place, where it's easy to overshoot the mark and risk a painful rebuff, so I think the mainstreamers bear some responsibility for any perceived shortcomings in my ways of demonstrating affection.