I don't think the narrator here only criticizes this tendency to look to the past. Indeed, the very way he uses language in speaking of it shows his own romanticization of it. Describing it as a "huge meadow which no winter ever quite touches" is quite lovely, contrasting sharply with the "bottleneck" that separates it from the present. There is some ambivalence in those lines: a participation in looking back even as criticizes doing the same.
Faulkner is demonstrating the human propensity to re-write the past. The old people wanted to pretend that they knew her well and cared for her, but this clearly was not the case. This theme is as much a storyline as is Emily's gruesome descent. In Part V, Faulkner writes:
They held the funeral on the second day, with the
town coming to look at Miss Emily beneath a mass of bought flowers, with the crayon face of her father musing profoundly above the bier and the ladies sibilant and macabre; and the very
old men-some in their brushed Confederate uniforms-on the porch and the lawn, talking of Miss Emily as if she had been a contemporary of theirs, believing that they had danced with her and courted her perhaps, confusing time with its mathematical progression, as the old do, to whom all the past is not a diminishing road but, instead, a huge meadow which no winter ever quite touches, divided from them now by the narrow bottleneck of the most recent decade of years.
The way Faulkner makes this one long nearly stream-of-consciousness passage is the way the older generation seeks to comfort themselves, and quickly. The men want to believe they had shown her social respect by including her in such activities as dancing, the women bring "store bought" flowers, a touch too little, too late; they didn't care enough to comfort her in life, and even in death their gestures are hollow, as are their feigned expressions of grief.
I think Faulkner is making a point about how one generation, if it doesn't learn to adapt, can literally be left behind. This happens to Emily. She is just clinging to her family's former social standing. In that way her present is always that of when her father still lived. Emily refuses every attempt to adapt to the changes in the town around her, whether it's refusing to pay property taxes or let the postman hang a mailbox to her door. This could well be one reason why people are so interested in her. She is a type of dinosaur representing the old southern way of doing things. Observe how Faulkner writes, "Then the newer generation became the backbone and spirit of the town" and Emily isn't able to fit in any longer because the times have changed but she hasn't. Later Faulkner also writes, "The front door closed upon the last one [generation] and remained closed for good." He, of course, is referring to Emily and the old Southern pride and attitudes she represents.