I take it you're referring to high school, not college. In college, breadth of knowledge is more emphasized (hence the complaints you see around here from the math/science students about having to take liberal arts classes).
I think some of the problem has arisen from reduced school budgets. There used to be quite a variety of classes offered in high school, different tracks for students with different objectives/abilities, and required "electives." (Yes, that's an oxymoron.) It comes down to a political issue. Do you go into a school in a poor district, that can barely afford to offer the basic classes it offers, and tell them you know most of their students will never go to college, so don't bother with college prep and focus on psychology instead? You'd have the ACLU knocking down the doors arguing you aren't even giving the kids a chance to go to college.
I don't really think there is any more emphasis on math and science than there is on English and history. Though, I tend to think the way those are taught at the high school level could be revised considerably. I know I didn't really appreciate any of those "great works of literature" until I was an adult. They just aren't that accessible to high school students because they deal with a lot of adult issues. And too often history is taught as an endless list of names, dates and places. To incorporate more about sociological issues and how they relate to the events would make it more interesting. I know I've always enjoyed trying to think about how people actually lived in the past, and much less about the name of the general who got the blame for a particular battle being lost.
Not every kid needs calculus. While I think every student who plans to go to college should be taught it, for those who don't, focusing on simpler, and more practical math, such as how to balance a checkbook, prepare a household budget, and comparison shop for the best price per unit rather than just the cheapest package of something, would likely be better received and more useful.
I'd love to see a major overhaul of or educational system. I think there is room to eliminate outdated courses and combine some subjects in a way that would be more interesting to students and more applicable to them. For example, that simple math for balancing checkbooks, etc, should be incorporated into Home Ec classes. Students really don't need to know how to sew their own clothes or bake cookies, but balancing checkbooks, understanding nutritional labels on foods, learning about babysitting/parenting, those would all be useful.
If classes weren't all taught in complete isolation from other subjects, so much more could be accomplished. Another popular class among those not planning to attend college (as well as many who are) is auto shop. Why just teach them how to pull apart an engine and put it back together? Give them some cost lists, have them figure out how much they're spending on parts, have them figure out how much time they are spending on the work, and using a fictitious wage, calculate their labor costs on the project.
Likewise, in math class, they could calculate whether it's cheaper to buy a clunker of a car and factor in all the repair costs vs a car that starts out with a higher initial cost, but has lower mileage and needs less repairs in the same 5 year period of ownership. Which one really costs more? These are real life applications that will really help a poor person break the poverty cycle by learning to be a smarter consumer. It's sure more useful to them than integrating area under the curve for a graph that has no meaning to them.
But, schools and school funding is determined on test scores. There's no room for an innovative curriculum that could actually be beneficial, because then they aren't prepped to pass those standardized skill tests.
I think we also fail to emphasize the right things in high school courses, including the science courses. For example, in biology, why on Earth are students required to memorize the kingdom, phylum, class, order, family, genus and species for 100 different organisms? I am a biologist, and have never had anyone point a gun to my head and demand that information, nor could I name all those organisms anymore (I would forget it from year to year between teaching it just like my students did, though with more years of doing it, more stuck in my head).
On the other hand, I think absolutely every high school student should learn something about political science. They will all be voters, and how can they be informed voters if they don't know how the system works?
Have I rambled and ranted long enough? I guess so.
Point being, even if the subjects are taught separately, they can be incorporated through this kind of bigger projects. 
