But Family Edition and Mini became a thing years after the launch (2011 Family Edition, 2013 Mini, unless you were Canadian, in that case 2012) , when the system was already a success / it was on it's way to retirement, and lived enough time for a revision to not being harmful.
Launching a new version of the system a mere year after the launch of the original model could have made consumers uneasy or angry, even more if this new model was announced shortly before the launch of the original system, like that GameSpot article shows (Written in 13th November 2006, Wii launched... on 19th November, 2006). It could kill a lot of the interest built towards your system and screw over Christmas sales too.
Not to mention those revisions that came years later were, for the most part, inferior to the original system, without gamecube game / accesory support for both, and in the case of Mini, removing component/S-Video/RGB video output, no online, no SD-Card support, and only one USB; and in no way they they replace the original model if you look for the best version of the system (as long as you don't look for 2006/2007 Wiis with weaker Dvd-drive, of course), unlike other revisions for other systems.
It would be like announcing the PS3 slim days before PS3 "fat" was launched, in a way. Of course, that's my thought if not wanting multiple "skus" was the reason for this not happening. It could very well be any of the reasons mentioned by tech3475.
That said, I didn't know about this, so as a trivia it's interesting.