The reason is that the items available in TBC

Phase 1 gear is certainly less engaging than Phase 1 Classic. This is because there's a greater number of loot items and more choices for you to farm or select from. Classic had only two healing weapons, and the KT Hammer didn't drop. While we're only in the beginning of phase 1, I have so many healing weapons to pick from. Each phase is also equipped with weapons that are unique to each phase. Every upgrade, despite the fact that there aren't many famous items such as Benediction or the Xerox, will bring good memories back.

The reason is that the items available in TBC are more balanced and offer numerous options for each slot. Vanilla equipment is not as memorable than TBC. However, people will remember broken items like HoJ Reju gem, HoJ edgemasters and others that are way more powerful than any other item that fits in that slot.

it's a bit more complex as "they did not know how to play back then". They intentionally created terrible high level items along with low-level or even end-game bis items that were conditional (based upon the event your gearing choices and your game plan) and allowed players to make "fun" and rewarding choices.

Although classic was min-maxed by years of pserver experience and incredible theorycrafters, Sims taught us that a lot of "bis" gearing options often were based on the guild's experience lengths and clear durations. Think of trinketswaps or threat against mit. Fire/frost resistance is another instance. Also, numerous trash skips and encounters with naxx were facilitated with niche products like the major recombobulator and smokey's lighter the bolt of Ramstein, and some the nifty stopwatches and gnomish concealing device and electronic gigaflux activator.

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