Yeah, but those are "schedules" not "timetables. For example, I might be willing to fly out to the coast on a 1 or 2 stop through flight, especially if the fare is significantly cheaper than the nonstop. And I want to avoid actually having to changes planes, as the stopovers are longer and there's always the risk of your luggage getting lost or your missing the connecting flight. The "schedules" on the airlines web site will give you this information, just as the "schedules" on the Amtrak website or app do. But I don't think any airline has timetables that let you figure out that Southwest runs a through plane from Manchester to BWI to San Antonio to El Paso. I think most passengers only care about getting from one point to the other with a minimum number of plane changes along the way. While I'm a timetable fan, too, it's possible that the only people who really care about them are railfans who like to figure out how the system works in detail. Of course, they should publish timetables, I'm sure they have them for the employees, it's a matter of transparency for the public that they be readily available, and it doesn't cost that much to provide them.The airlines think that there's no alternative and the cattle will take what they're given.
But the local AIRPORTS publish the schedules for the planes leaving that airport, because it's crucial marketing for a smaller airport. If they don't, people will just drive to the larger airport and never realize the small airport has suitable flights. (Google Flights's "search nearby airports" and "see all destinations from this airport" options help.)