You have likely heard the saying, “It’s easier to ask for forgiveness than it is to ask for permission”. What you might not have heard, however, is that the quote isn’t really the whole story.
The real story is:
It’s easier to dismiss something you haven’t invested in then to figure out what do with something you already have.
Don’t believe me? Why does bad code live for so long in every project I’ve ever been on? The reason is simple. It’s harder to do something about it once it’s already been done. You clearly can see and understand the cost in fixing it but in the back of your head you know it already works. If you fix it, you are committed and you can’t back out. You gotta take the whole thing in and own it. Instead, what do most developers do 9 times out of 8? We complain about the code as being bad, and an eyesore and evil… because there is literally no investment in actually fixing it.
But don’t feel bad. Customers do this all the time too. If you asked a customer if they wanted: security, tests, new features and delivered on time… who wouldn’t say no? If you have no concept of the actual cost of ownership on any of those above, why not say yes? The problem therein however is that they never really invested in any of them. Once deadlines get strained, or features aren’t finished, or quality is going south… what are the first things thrown away? The point is that it’s not until you apply a real pressure to something do you find out what matters and what doesn’t. The first things to go are ALWAYS the things people aren’t invested in. Good, bad, indifferent.
@"figurative"; 
i don’t necessarily agree with all the points in this article below, but it brings up an alternative reason to having “bad” code lying around:
http://www.joelonsoftware.com/articles/fog0000000069.html
and for the record, whenever i get a chance to “fix bad code”, i do it. and so do most of my coworkers. perhaps, they are the exception.