Probably around 80% of the playerbase gets some sort of class-based or race-based infravision, the rest have an easy enough job with finding a wearable glowing object to get by. I don't see much reason for paladins, who focus on battling evil and protecting the innocent, to suddenly learn a spell that has little to do with their goals.

That being said, there's already a generic infravision-type skill that anybody can learn who does not already have that ability. Work on your observation experience to gain it.