hardset nipples, I think you're oversimplifying things a little bit, and are also in at least one case factually incorrect. Let me explain:
1) You are factually incorrect in that, of the races you list as both not having elites and not having major sponsors, I know firsthand off the top of my head that at least two of them have well-known sponsors paying in the six-figures annually to title sponsor the event. Others may as well. It seems, then, that in at least some cases sponsors are willing (and, in fact, want) to associate themselves with events that don't have elites, believing they will reap benefits.
2) It seems that you're conflating "large/fast elite field" with "large amount of media coverage." While New York, Boston, Chicago, and maybe a couple other marathons in this country Houston, LA, possibly Twin Cities if it's hosting a national championship of some sort) are covered as elite sporting events, many others (including some of the ones you listed) are covered primarily as city-wide festivals, celebrations of fitness, or as a collection of human interest stories. Again, I know firsthand of at least one of the aforementioned races being much happier with both the quality and amount of media coverage it has received since it eliminated its elite field.
3) I do think you're discounting pretty significantly the value sponsors place in reaching 15,000-40,000 non-elite participants (plus an additional 20,000-60,000 supporters who come along to the event to support the non-elite runners). Studies (and I'm sorry I don't have specific citations--many of them are behind a paywall at sportsbusinessjournal.com) show that participants in marathons and other major participatory events have very high sponsor recall (ie, being able to name event's official sports drink, apparel provider, car, insurance company, financial institution, nut, or whatever else), tend to have strong positive opinions of these sponsoring companies, and are highly susceptible to advertising surrounding their events. That's a lot of folks with positive associations--and that sort of goodwill has value to customers.
4) I think you're overlooking to some degree how much scope matters to people. If I don't know the New York Marathon is going on, and I walk outside my brownstone in Brooklyn to go to the market and see 20 really skinny guys not wearing very much clothing run by pretty quickly, and then on the way back from picking up my fair trade bananas and coffee see 15 more really skinny women run by only a bit slower then the men, I might wonder, "Huh? What's that about?" But if there is a steady stream of people running by, and hundreds of other people on the street watching for them and cheering for them, I'm a lot more likely to stop and watch part of the event (if only to find out what's going on). And if I stop to watch even a bit of the event, I may see sponsors' logos and messages; and the scale matters in whether I'm likely to stop and watch an event or not.
5) Your claim that elite fields are paid for by title sponsors seems to imply that all races' business models are the same (although you acknowledge that isn't the case in your brief discussion of the Disney and Nike Women's Marathons). They're not. Some races (even some mid-sized-to-large ones) are non-profits with missions of "improving community fitness" or something like that; these races are unlikely to shell out for elite fields even if they sign a title sponsor (some, however, might, if they believe they could better achieve their mission through utilizing elites; most non-profit races discover, though, that this doesn't generate a great ROI). Other events, even some for-profit ones, believe in supporting elites regardless of the status of their title sponsor; obviously, a drop in revenue means having to restructure the budget, but depending on the priorities of race management, at times the race might decide to cut other race elements (bands and entertainment, fancy awards, etc) before they cut elite support. A race still has to believe it will do okay financially to be able to do this, but I know several RDs who are of this mindset. Races' business models differ.
Okay, sorry, that got pretty long. While I don't believe you're entirely incorrect, hardset nipples (except in a couple very specific cases, as I pointed out), I do think, whether you intend them to or not, your posts imply a black-and-white, the-value-in-events-to-sponsors-is-in-their-elites-rather-than-the-masses viewpoint, which is myopic. There is value to sponsors in events having good elite fields (especially for events such as the World Marathon Majors, Houston, LA, Twin Cities, etc, which have a larger part of their brand equity tied up in their elites), but there is also substantial value in the thousands (or tens of thousands) of non-elite runners, spectators, and volunteers who in some way participate in the event.