Because skill feats are tied to skill proficiency and those increase at odd levels. Level 2 just happens to be the level you can become expert at the erliest (and only if you're a rogue).
Most classes get Skill Feats only at even levels, but Rogues get a Skill feat every level, so it matters at least for them.
So basically, they made the number apply to the rogue since it's THE Skill class. And because those numbers aren't wrong for other classes.