The original WoW dev team, circa 2001-2007 were radically different people to the current Classic dev team. Different people, different ethos, different values different methodologies.
The original team, featuring iconic figures like Mark Kern, Chris Metzen, Rob Pardo, Jeff Kaplan, Tom Chilton and others were self-confessed gamer geeks. Their mission was simply to make the best, most fun, most engaging game ever created, founded upon the backbone of the existing lore set up in Warcraft III and taking inspiration from earlier MMOs - but creating something with far more mass appeal.
In this they largely succeeded.
But these people no longer make the game. The modern game is designed and implemented largely by committee and the core ethos is no longer ‘Let’s make the best, most fun, most engaging game ever created’ but: ‘Let’s take this existing product and monetise it to the highest extent possible, and then see how far we can push it without alienating all of our players.’
The current classic devs are part of that retail bunch, part of the ‘monetise everything’ mindset. They are retail devs, with a retail mindset and intent upon creating a retail game shoved inside a superficially classic shell.
They have used the ‘boiling frog’ method to implement increasingly predatory and opportunistic systems within the game - beginning with the hated level boost, then moving on to cash shop items and finally the dreaded WoW Tokens.
Nothing represents this mindset more than Cataclysm. It’s the pinnacle of the 'Strip the game down to it’s basics, streamline everything, cut out anything that slows 'm down, rush 'em through the game at breakneck speed, get ‘em hooked with repetitive end game and shiny loot and then milk their subs for all we’re worth.’
They could have made a Wrath or TBC client - they chose not to, because that would be of little or no benefit to the quarterly earnings.
And that’s where we are now.