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Evasion boosting is self perpetuating in a way many other boosts are not.
Sure, you can boost your crit chances, but you still have to deal with "losing" a turn and planning around your opponent trying to stop you. It also only works on a few mons and therefore is easy to see coming, making it harder to pull off without some thought.
Evasion boosting, however, inherently makes it easier to keep boosting evasion. Every time you use an evasion booster, it makes you harder to hit, which gives you better chances to keep boosting, which gives you even better chances to so on and so forth until you're basically unstoppable. It's also available on every single mon in some way.
