Something that allows funneling resources. You need a character or friend or AH that can dump like skins or cloth into gear, farm some dungeon/rare mob dropping high level blues etc. If you have excess gold you can buy all mats needed to level it up, get rare recipes and just live from enchanting fee (but there are still oils as a consumable or DE mats as an income from AH).
A mage is good with tailoring as mage can AoE farm humanoids for cloth. Single target classes, even tanky ones can focus on farming blues into large brilliant shards or leatherworking into Cenarion Circle blue bracers into those shards. And there could be more to that.
Also people going enchanting do that close to max level while having 2 gathering professions while leveling for income/vendor income/future professions.
Depends. It was a new game, not everything was polished/thought over and over and there was less power-play knowledge so over-benefiting from no-skill-DE wasn’t something was quickly noticed back then. That change was likely mostly to patch-up that hacking profitability.