If you have a strong enough urge to learn something and your class or textbook doesn't teach you, you will take it upon yourself to do so; and without guidance, you will probably do so wrongly. That's my guess as to what the explanation is. If nothing else, it's why I sought many of these things out (the difference being that I didn't even have a textbook or class at that time; though then again, maybe that's not a difference).
Personally, I have always had a strong desire to make my manner of speaking more complex and expressive. I'm really bad at vocabulary, so the way I've tended to prefer to do that through most of my life has been through grammar and tone. I can't tell you how hard it is to not attempt to use and understand a grammatical construct that I understand very little. I suppose it's like seeing an oasis in the distance. Even if I've got a less desirable but functional water source where I'm standing and can't tell whether what's in the distance is an actual oasis or just a mirage, I really want to get there if it won't kill me to do so, at least to see if it's real and try it out.