Yeah it’s a classic example of the adage about the road to hell being paved with good intentions.
The original talent trees provided a lot of options, but in reality, from a math point of view (and RPGs, from table-top on, are about math in terms of their mechanics … math and probalities), there was only ever one best choice, and perhaps in some cases 1 or 2 “borderline viable” choices, and everything else was “wrong”/bad. In other words, the plethora of choices served as a “noob-check”, in allowing some people to mess up their character’s performance due to ignorance and not be able to fix it cheaply, while allowing others who were meticulous about their research (at the time when info was less easy to find than today) to really “create distance” between themselves and the “average baddie player” even when picking talents. This wasn’t ideal.
What happened next is that as it became more widely known what were the “good” specs and what were the “bad” ones, the playerbase as a whole migrated towards the good ones and away from the bad ones. As a practical matter, the talent trees stopped acting as a “noob-check” for the most part, and were being min/maxed anyway, because information was becoming easier to come by, and players were optimizing their choices. The addition of transparency mechanisms like the armory, and then later out of game systems to verify a player’s choices added to the effect of most players more or less stampeding into certain specs and away from other ones.
That’s the context in which Blizzard simplified the talents – the old talent trees were mostly pro forma anyway in that most people were picking cookie cutter specs from Icy Veins and so on anyway. So they were simplified.
In tandem with that, the content was adjusted around the idea that most people were, as a practical matter, min/maxed anyway in terms of spec – because they were, and so in order to provide something of a challenge to the majority of the players, the content was adjusted around the assumption of the majority of the players min/maxing. As a result, however, if you were not min/maxed, well … the content became a lot harder for you.
No step along the way was made maliciously. However, it all added up to a system that now is centered around min/max. To be fair to Blizzard, the players got there before they did, in that it was the players who made the original talent trees mostly irrelevant by creating things like “meme specs” and by crowding into a narrow band of “viable” specs anyway.