Simple.
The one you make is for you only, and maybe a few of your friends who also DM and who adopt your setting. It's a true homebrew, designed and used at home and (probably) never intended to be any more than that. Also, the only critics you have to answer to are yourself and the people at your table - and maybe the tables of a few other DMs.
The one WotC makes is for (they hope!) everyone. It's not a homebrew, in that it's specifically intended for mass consumption; but neither does it set any baseline defaults in the game system due to being its own thing.
Eberron ceased being a true homebrew the minute WotC released it as an official setting.