Because some people rather squeeze and experiment by using the least amount of money involved (or none at all) possible rather than buying something completely new that could cost heaps heaps more. I for one am of these people. Sort of like overclocking your computer, why pay more when you can get to the same performance for $0?
Fair enough but to me the bass is their defining characteristic. If you try to control or reduce it then you've lost the point in my opinion.