I think that's the reason. So many people found the even one or two levels of exhaustion so debilitating* that they effectively retreated until restored once they hit that (making the rest of the scale superfluous). It's the situation of a damage-scale to dangerous with which to engage. Symabaroum and Wraith: the Oblivion have the same issue: permanent corruption was so onerous that players don't go near the point where they risk gaining any (making most of the scale leading up to it wasted).
*In exploration/survival situations, even one level got you disadvantage on all the skills you would use to explore/survive, making people highly resistant to pressing on.
Hmm. My recollection is that that was kinda all over the map. Looking at 1E and BX, in BX most of the resolution information is in the Player section, but 1E puts most of the rules of play in the DMG.
He said that '[they] don't want their design to chase phantoms.' Unless you think the game design chases individual people, your interpretation of his comments literally do not make sense. The second half of the sentence clarifies what phantoms are in contrast to ('real desires held by a large number of players.'). He seems to be, in effect, saying 'we're looking into the possibility of alternate classes, but we are still in process of making sure that it would address the desires held by a significant number of people'), which is a perfectly reasonable position to have. The way he said it is a little tin-eared and clumsy, but it is unsurprising both that a gamer might be a little socially inadept or that someone shooting out a quick tweet on Twitter might accidentally step on toes (seems to be the reigning stereotypes of each thing).
More broadly, none of that has anything to do with whether the creators have big egos or not.