There’s a lot of engineering specific data listed in the official post that shows off the challenges facing Classic.
Blizzard has been working on launching World of Warcraft servers that just run a classic version of the game, back before all of the updates were added to the world… of Warcraft… over the years.
Modern WoW is a lot friendlier, a lot more streamlined, and feels less like a wild and dangerous place.
Core features like Battlegrounds were introduced in patches after WoW’s original launch, and class design similarly changed over time.