I remember hearing about this somewhere, but why exactly is that, again? Do we have any sources on why that is the case?
Well, for the record, LEGO does seem to often produce modified versions of some parts for no easily identifiable reason…
Just giving this as an example, I see no practical reason why they produced this particular mold, if they could have just used the regular brick with Technic pin holes instead. And this is just one of many examples. The point is, LEGO does seem to often modify pieces even when it may not be entirely practical to do so. What internal factors go into such decisions we cannot know, but we cannot rule out the possibility of getting modified Mixel joints either.