They are intelligence checks because those skills are governed by intelligence. Just because DEX and WIS are your primary stats doesn't mean every skill your class gives you will key off those stats. Rogues are chiefly DEX but can grab skills from INT or CHA just as easily.
It seems like Larian tried to make the ranger more of a skill monkey like rogue and bard, but without expertise they'll never be especially good at it which is a shame.
Granted ranger is a pretty solid class right now. The favored enemy skills are more like ribbons than things that majorly define the class. Which might change. We don't know what Larian has in mind for the ranger as they get more levels. Favored enemy is a class feature so it should get improvements as you level up.
