Unfortunately the problem is that "unimportant" facts and skills are all over the place, and are not limited to subjects outside your interest. I'd bet you might even learn useless things in classes on subjects you are interested in. Combine that with the apathy for teaching and increased focus on testing well for federal funding (in the US), and it's all useless.
(On a less cynical day, I'd say that eventually taking all these "useless" classes in HS might come in handy some day, you never know. I realized what I had gotten out of it the moment I left. I had an art history and ceramics class that's prompted me to look for a pottery studio near my home to continue on because I love making cups. The scant amount of chemistry I've learned bored me in HS (and I thought it was useless...) but it gave me a foundation in college to take so many chem classes I'm considering a double major in chem and CS. My last HS phys ed teacher over the course of a year never let me give up no matter how badly I was doing - something I've never had happen at the gyms I've been to with all the trainers I've seen. His voice is the voice I hear internally encouraging me to keep on running/swimming/working out or to even get my ass out of my chair after sitting in it all day. All these little things I thought were stupid ended up making a fairly large impact on my life. I wonder if I'm the exception to the rule.
I might also note I actually ended up dropping out of HS after my sophomore year because I thought going to college early would help me more with my interest in "computers" since I still had to take some number of "irrelevant" classes but I could focus more on my interests. I don't regret that, and occasionally I wish I had left earlier on, but I can't deny that what little I did do in HS has impacted me.)
(On a less cynical day, I'd say that eventually taking all these "useless" classes in HS might come in handy some day, you never know. I realized what I had gotten out of it the moment I left. I had an art history and ceramics class that's prompted me to look for a pottery studio near my home to continue on because I love making cups. The scant amount of chemistry I've learned bored me in HS (and I thought it was useless...) but it gave me a foundation in college to take so many chem classes I'm considering a double major in chem and CS. My last HS phys ed teacher over the course of a year never let me give up no matter how badly I was doing - something I've never had happen at the gyms I've been to with all the trainers I've seen. His voice is the voice I hear internally encouraging me to keep on running/swimming/working out or to even get my ass out of my chair after sitting in it all day. All these little things I thought were stupid ended up making a fairly large impact on my life. I wonder if I'm the exception to the rule.
I might also note I actually ended up dropping out of HS after my sophomore year because I thought going to college early would help me more with my interest in "computers" since I still had to take some number of "irrelevant" classes but I could focus more on my interests. I don't regret that, and occasionally I wish I had left earlier on, but I can't deny that what little I did do in HS has impacted me.)