Let's be real here and imagine this from a legal standpoint:
What happens if parents don't know about parental controls (you scoff, but this happens with probably at least 75% of the parents of this generation of children)? They see that this is an "E-for-Everyone" title, and they're "little angel who wouldn't do anything wrong" has been begging for it for months, so the parents get it for him/her. The kid pops in the disk, goes online, and the parents walk in and hear a very racist/sexual conversation going on in voice chat. Now, the parents won't do anything to the child, because, you know, he/she OBVIOUSLY would NEVER engage in such scarring activities, so they go straight to the top and sue Nintendo for the ability to use the chat feature with total strangers (or at the very least not making the cover art "USE PARENTAL CONTROLS" in bold block letters)
Now I know that this definitely isn't the main reason that it was axed/not included in the first place, but I guarantee it was at least a key factor in the decision. Yes, it could have been handled better, but really, I don't blame them for wanting legal amnesty in this situation