I don't see the big deal. Now the marathon is like every other event at the olympic trials. You don't see a lot of 1:54 800 runners at the olympic trials (that is the equivalent according to the mercier score calculator), so I don't see why 2:22 marathoners should be mad because they are not allowed to compete. Actually, the B standard in the 800 is 1:48.5 and if you convert that point value to a marathon you get 2:14 so actually 2:19 is still very fair. I think everyone just needs to man up and stop complaining.
ps I randomly picked the 800, you could make the same argument using a 10.77 100 or a 3:53 1500 etc
Truthiness, I like your general type of argument/perspective. But your analogy has real limitations. First, as the duration and distance of events gets longer, events change in important ways. For instance, world class times in the sprints have improved far less (in percentages) over the past several decades than have times in the distances. Similarly, some teenagers run essentially world class times in sprints but none do in distances. These facts suggest that distance running, and marathoning especially, is much more dependent on training duration and the unknown "trainability" of any particular athlete. Thus, the absolute performance limits for any given individual are much less clear in distance running than in sprinting. Thus, a 24 year old with say 6 years of high-level training with a 2:20 marathon PR might have a small but genuine chance to eventually become a 2:10 marathoner (e.g. Sell). By contrast, a 24yr old 800m man with 6 years of training who has a PR of 1:50 has essentially no chance of ever running 1:45. So this is one reason why it is more important to keep the "qualification carrot" available for marathoners and not for sprinters or middle distance runners. And, of course, sometimes marathoners with roughly 2:20 PRs will show up at the trials and perform remarkably better than that (e.g. Lehmkuhle). A remotely similar jump would never happen in a sprint or middle distance event. In sum, there are real potential benefits of allowing 2:20 guys into the OTs, but there aren't for allowing 1:50 guys into the 800m OTs.
Second, from the perspective of costs, your analogy has limitations. Vastly increasing the number of 800m men at the OTs would dramatically slow down the meet. Having 300 or 100 marathoners barely changes the length of the event. Yes, there are other costs besides time but they don't seem great to me, especially if the B guys pay their way.
Finally, marathoning is unique is that large fields have been a regular part of major marathons for many decades. The spectators (not surprisingly) seem to like it. This obviously isn't true in other events.