SCH already learned every other Regen Spell before WHM and I will dismiss the point that WHM existed long before because I am talking about the level both classes learn the spell, not the point in time they've been created.
SE won't give SCH and RDM Cure 5, which I guess you would cry that much louder if they did. So take it and be happy that SCH got it. WHM doesn't need regen spells, they're cures became so much more MP-efficient and the concept of regen, namely hqealing over time, does fit a Scholar, who can also throw out heavy damage over time, much more.