The notion that there always must be a set of miscellaneous sounds churning along in the background of a scene just because that’s the way it is in real life* is a fundamental misunderstanding of the way film storytelling works. A film can’t replicate reality, and shouldn’t try. What it can do, much like a dream, or more to the point a magic trick, is to stylize reality in ways that can enlighten and entertain.
Putting backgrounds, AKA ambiences, into a film is often (but not always) the least productive work done in the sound effects editing room. In the conventional workflow these are typically the first sets of sounds a designer or sound editor adds to a scene. Therefore, the work is done when she/he is least familiar with the film. Wind, traffic, birds, insects, rain, thunder, room tones, machines, etc…. are often added without paying much attention to where dialog sits within scenes, and with little or no knowledge of the music that will eventually inhabit the scene. They are also usually added with very little input from the film’s director.
Ambiences are most often emotionally neutral, which rarely serves the story, and instead simply tends to mask or mute the drama or the comedy in a scene. It’s basically noise, not necessarily useful noise, and in my experience directors are much more likely to ask that it be removed in the final mix than they are to ask that it be made louder.
I would propose that in most cases ambiences should be the last sounds added to a film rather than the first. Lots of time and energy would be saved, and the background sounds that ARE added will be much more likely to serve the story rather than being annoying, obfuscating wallpaper.
*The wind rustling the leaves in the background of a real conversation is often noticed by one participant in the conversation but not another. The fact that a microphone recording that conversation also simultaneously records that leaf rustle is irrelevant to the storytelling value, or lack of storytelling value, of the leaf rustle. If the leaf rustle makes the scene more plausible then it may have value. If the leaf rustle has some story connection to one of the characters it may have some value, or if it evokes an emotional response, or if it muddies the sonic waters in a useful way. But adding leaf rustle simply because there might be leaves rustling in that scenario is not imaginative, and may do the story more harm than good.