Isn't it because in the games previous to WoW, low level characters with really powerful gear were called twinks?
Below, I bolded games in which have references to twink, most came before WoW.
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Wikipedia - In computer role-playing games and MMORPGs, twinking refers to outfitting a new character or player with items or other resources that are not normally available to new or low-level characters. A twink in this usage is a type of powergamer and munchkin. The term can also refer to the twinked character itself (e.g., "My twink has all the best gear.") In its most basic definition, a twink is a character with better gear than they could have easily gotten on their own.
Twinking was once very common in the CRPG Guild Wars, when players would have their low level characters taken by high level characters to end-game areas to obtain the best armor, weapons, and skills available, as Guild Wars does not have a level limit on such things. These twinked characters would then return to low level PvP areas to fight significantly disadvantaged opponents. This practice became so proliferate that the Guild Wars development team introduced a patch prohibiting characters with high level armor entering beginner arenas.
One game in which twinking is common is Anarchy Online. All character classes have skill-enhancing "nanoprograms", the equivalent of spells in fantasy MMORPGs, some more in demand than others that allow you to boost various skills, makes twinking easy. Also as large number of items in game don't have level limitations and due the large variety of items, low-level characters are often able to equip equipments meant for much higher level characters.
The practice of character twinking can also be found in World of Warcraft, where players are divided into level-brackets in Battlegrounds. By using above-average equipment otherwise difficult or impossible to obtain by other players in the same bracket as well as using end-game enchantments, twinked characters have a significant advantage over non-twinked opponents in terms of survivability and lethality often having triple the health of a non-twinked character.
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There are several possible etymologies for the word. It may not have been derived from a single source, instead evolving from multiple convergent usages. Its exact origin is unclear.
The gay-slang usage of "twink" has also been suggested as a likely origin.[1] One of the unofficial connotations of this usage is "a young/inexperienced person who can outfit himself fashionably because of financial benefits from an older/experienced sugar daddy." This parallels MMORPGs, where in-game money is a strong limiting factor in the virtual economy and gear is usually in the form of clothing and jewelry.
The word "twink" appeared in the Ultima Online: Renaissance playguide in the glossary of terms. It was asserted to have a meaning similar to its current one, but also included powerlevelling.
On Sojourn MUD, which several creators of Everquest played, "twink" was alternately used to refer to powerleveling and metagaming. As the text-based game was founded in the 1970s, this use of the term may predate later uses.