It appears to be the trendy academic thing to do in academic circles, ever since Adolph Jülicher protested almost 2000 years of banal Christian allegorization of these stories, to resist the idea that parables should be read as allegories.  Jülicher and those who followed him insisted that they be read more as simple similes, as "illustrative parallels," instead. 

At first, I found myself in sympathy with Jülicher's position, since I am uncomfortable with the Christian rush to derive allegory—and from allegory, meaning—from Jesus's stories. The traditional, allegorical meaning seems to have eclipsed the literal one, to the point where listeners are unable to hear the story itself. The shorthand "Good Samaritan" has rendered invisible the enigmatic details of the story of a man injured on the road to Jericho. 

That said, my position is that one should always approach the parables first as what they are: stories. One should hear them without the heavy hand of allegorization and traditional interpretations hanging over them, and let the characters and the story be seen for themselves before one reduces them to symbols. 

A hard stance against allegorization, as it turns out, may actually have theological, rather than literary, motives. As Stern notes, regarding Jülicher's school's insistence that parables are, in fact, the opposite of allegory:
 

First predicated by Jülicher, partly out of the conventional nineteenth-century view of allegory as an artificial, intrinsically inauthentic mode of language, and hence as a particularly unsuitable medium for Jesus' divine speech, this belief has had a powerful impact on all subsequent research on parables... In Rabbinic scholarship, in turn, the mashal's allegorical features, particularly during the Amoraic period, have been interpreted as some scholars as evidence of the literary form's degeneration, its fall from "parabolic purity." 

In other words, the impetus for departing from the traditional allegorical reading of parables is not in the interest of hearing them afresh, of acknowledging their ambiguity, of hearing them as stories, or of opening them up. It is only the belief that one-note traditional interpretations were correct in their strictness, but wrong in their type. It is not driven by a desire to hear the words for themselves, but to hear them as divine speech.

Moreover, the assumption that Jesus's parables represent some sort of "pure" divine speech has been used to characterize the development of Jewish literary forms after his time as a degeneration or corruption of a divinely inspired form. It's nice when the world acknowledges that Judaism didn't freeze into an archeological artifact as soon as Jesus came along, but characterizing the living and evolving culture of the Jewish people as a degeneration of a pure Christian prototype is just another form of supercessionism.

Stern points out that the Hellenistically derived categories of "allegory" and "parable" are simply the wrong paradigms from which to approach the mashal:
 

Granted, if the term allegory is taken in its largest sense, to describe all discourse that is referential, then the mashal possesses allegorical features: the characters portrayed in its narratives, the deeds those characters perform, the situations they find themselves in—all these routinely refer in meshalim to something beyond themselves. But even if the mashal overlaps with allegory in this respect, it is not itself a mode of literary discourse as allegory is, a type of speech that says one thing and means another. Rather, the mashal is a literary-rhetorical form, a genre of narrative that employs certain poetic and rhetorical techniques to persuade its audience of the truth of a specific message relating to an ad hoc situation.