This is a design feature that has carried over from old trainers. Back when engines were low on power and instructors were few, the designers figured that if the plane was climbing slightly the guy trying to teach himself had a better chance of not crashing right away

Newer 40 sized engines perform like the old 60 sizes used to. But trainers are meant to be flown slow so with the excess power they climb. Almost all trainers I have seen needed one of the fixes above(all will work) even flying at slow to moderate speeds.