CBS shorted original TAR after TAR 12 because of several factors. First was to reduce filming costs in a period where travel costs were going up rapidly at the time (tied to the cost of jet fuel, and other transportation costs. Keep in mind there's a lot more traveling to film the show than just the teams and Phil. Second was the problem in fitting a 13 episode season into the CBS schedule especially with the dead periods of US television and the special scheduling CBS faces due to certain other programming. A 12 episode season worked better from CBS' point of view.
Third, the lack of popularity among many viewers and teams of the NELs. The schedule in two of the last three seasons to have the first leg as a NEL actually solved a issue in that one complaint has been that viewers didn't get much of a chance to learn about the first few eliminated teams before they were, well, eliminated.
It's pretty clear now that the 12 leg, 11 team model is here to stay, and when it does vary, it is an indication of something different in the game such as a start line elimination, a double-leg, or a double elimination. It's pretty clear that CBS wants the production cost controlled, but with these last couple of seasons, CBS has eased up a little in order to accommodate the show's need to go to new out-of-the-way places, and to design tasks that are not generic.
So while as a fan, I would love longer seasons, with more teams/legs/countries, akin to the early season format, I realize that isn't going to happen. The primary reason why Israel follows its unusual format is to amortize the production cost by using everything they film. Original TAR has a fair number of route markers/tasks that are never aired, but that's more easily built into the production costs (but they do try to avoid unnecessary tasks that can't be used but there are a fair number of route markers that don't cost much to film that end up not being aired as a result of the editing process.