Probably. Something to understand is that a lot of later code is written based on earlier code and rewriting earlier code to "fix it" can have unforseen consequences and break something completely unrelated creating a much harder to fix problem because fixing what obviously broke because of the fix might require chasing down what actually is causing the new problem somewhere in between the newly written code and what just broke. Call it a ghost in the machine problem.
I imagine they could fix the earlier code, but consider that it took a year to re-code Forge with better code and less clutter and Minecraft is likely a lot more complex than Forge. I don't want to know how long that re-code would take.
So, sometimes, as Cadiboo said, if it ain't broke, don't fix it.