I don't get it.
Why not just put the character name and be done with it?
If a character shares a name, then just put the artist name next to the character

To me, [NAME]_(disambiguous) seems pointless in my opinion. So why do we have it?

Because people don't put the artist name next to the character?

It's there to let the tagger know that they need to use a more specific tag.

For example, let's say that someone uploads an image of their dog fursona, named Rex. And because they don't know what they are doing, they add the tag rex to the list.
Well, thanks to an alias, that tag becomes rex_(disambiguation), telling the tagger that they either need to pick one of the many characters already using that name or to create a new character tag.

ah I see it makes sense now. So basically they're leaving it to us to basically clean it up.

_(disambiguation) is basically saying "oi put the artist name next to the character for me"