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(I at once cannot believe yet entirely understand why they made Marina the wannabe idol).
The problem is that the anime's writing wouldn't do anything worthwhile with it- you would likely just have a less-distinct version of Special (notice the non-qualitative). Ash as the eternal lead gives them one less character to write from scratch while creating and carrying a vested interest in the returning viewing audience that is clearly still paying dividends to this day. A lot easier to bounce from a bad arc to a better one (Black/White to X/Y, from everything I've head) with a lead character that simultaneously does not have to commit to anything yet a bunch of people want to see return to form. When that happens in another toyetic series you get Yu-gi-oh! ARC-V and people just QUIT.