Wizards actually can use multiple Winds, and can even do so safely (or as safely as magic gets) as long as they don't have Arcane Marks and they're careful to 'detox' from one before using another. It's just rarely done because you're almost starting from scratch with each new Wind, and if you ever get an Arcane Mark that's it, you're locked in to whatever Wind gave it to you. It's not something that can really be researched, it's already a well-understood phenomenon.
In contrast, Elven magical techniques are based around using Winds without being shaped by them. This is a very long process and requires mastering one's emotions, which is why conventional Elven wisdom said it couldn't be taught to humanity. Teclis stripped out all the 'without being shaped by them parts' to speed up the learning process, grasping that many humans would think that gradually becoming a living avatar of a single Wind is rad as hell, rather than a tragic failure. The downside is that it makes any human High Magic virtually impossible, as they'd have to reach a mastery of all eight Winds separately and without ever acquiring an Arcane Mark just to get started, all within a standard human lifetime.