Because to override what is shown in-game in favor of a new hypothetical form of evolution to justify a preconceived notion of a timeline is to exit theory. If you have one connection of a Rito in SS, MC, FS or OoT, I'd love to see it.
Placing the Rito before Wind Waker does not override anything we see in game. We see Rito that are related to Zora in WW, sure. We also see hints that Zora exist off screen, in WW, and the following games (Items, shop menus, and the like). Plus, the Rito we see now are very different from what we see in the WW line. This means that allowing the Rito to exist in the time of the early games in the time line changes nothing from what we do see.
As far as preconceived notions go, demanding that the Rito only came from the Zora, in the time of WWs backstory, and forcing all other theories to fit that, departs from theory craft, in favor of dogma. That theory is older than what is being talked about now, and does not include anything we see in the new games. The idea that the Rito are older than WW is based on the new games.
Finding ways to make what we see in the canon is the very core of theory craft, whether you like it or not. For instance, I may not agree with the main idea of the thread, being a fourth parallel timeline, but I still take it seriously. It has as much merit as a singular linear timeline. Agreeing with a theory, pointing out flaws in the theory, disagreeing with the theory, and trying to shoot it down with flawed arguments are vastly different, and are not mutual to each-other in any way.
And, as I have said, it's a possible connection between the Rito and an earlier game. In Skyward Sword, there are statues in the Skyview Temple that are far closer to the current Rito appearance, in comparison to the generally assumed Loftwing. It may not be a smoking gun, proving without a doubt, that the Rito absolutely had to exist, but it's a stronger case than trying to say that they couldn't exist just because we don't see it.
Better writers aren't going to fix pre-existing issues from the past 40 years. You're missing the point entirely and I already said this isn't meant to be a "fix" to the timeline.
This is true. For that mater, I don't think the writers are the problem at all, simply because the games keep drawing more and more fans in. If the writers were genuinely bad, the franchise would have died a long time ago.
With all the flack you are receiving over this idea, I'll just point out that while I don't think the fix is necessary, I do agree that it could work. In an older theory I talked about how having a time split as it is commonly explained in Ocarina of Time, it should follow that we would have a split in Skyward Sword. Just before the final battle, Link has the opportunity to go back and do more things, before stepping through the portal. Demise "winning," no mater how brief from the player's point of view, does not causally force Link through the portal, otherwise Link would simply leap through in the same cut-scene. If the player has a choice, Link has a choice, a time split is possible. Not to mention, Demise declares that he has conquered time. In that time between Demise going through the portal, and Link choosing to go through (by Ocarina of Time split rules), a whole history of Demise winning un-contested would evolve. Only when Link chooses to step through the portal would we get the time split where the other games take place.
Long story short, If there is a place in the other games to connect your fourth timeline to, I think it would be that moment of Demise's victory.