It is a mix of “because we can” and “lets see what this baby can really do!”. Hackers want to explore the limits of their skills and of their hardware. There is also a strong, “All information should be free!” element to it. The easiest way to gain a true hacker’s interest is to lock something up.
However, as @anartist points out, there are those that the mainstream calls hackers who at least in my opinion aren’t. The most common are Crackers. They are the ones that want access to a bank so they can transfer funds to their account, or seek to just cause damage, possibly for a reason or maybe just for kicks. These are the “Black Hats” spoken of above, and they are assholes. Skript Kiddiez are like Black Hats, only without any real skill of their own. They generally just like to one-up each other with petty vandalism for the sake of being a nuisance.
Then there are the ones who like breaking the copy protection/registration on software because they feel it is overpriced. In a sense, they are not wrong; Windows only costs a few cents, but the license to run it legally costs a few hundred dollars. Or maybe it’s just because they feel that, once you buy a movie or album, it should be yours to do with as you please, including making a backup copy in case your original disc gets damaged/lost. These people can be white, grey, or black hats, depending. They also often have little/no interest in the systems of others, so they don’t “hack” in the way that most people think of.
Somewhat related are the people who see a commercial product and seek to replicate and possibly enhance it’s functionality, often for free. These are the people who brought us Linux, OpenOffice, GIMP, and many other cool bits of software.
Then there are “hardware hackers” trying to eke out the last bit of performance from their rigs, or possibly get it to do things it was never originally designed to do. These are the guys who overclock their CPUs or write applications that no commercial entity felt was ever necessary.
There are other types as well, but I think you get the gist. And be careful when you say “hacker” and that is kind of a loaded term thanks to decades of misrepresentation ;)
@Ron_C No. However, if you lock your underwear drawer, they will likely try to pick the lock and then lose interest once the drawer opens. For example…
@pezz There is more to it than being good with computers. Hacking is a mindset, and often incompatible with what most employers want from their IT staff. Free will and curiosity are actively discouraged in many places, and that sort of stifling environment is a fate worse than death for many hackers.
@Tbag @Blackberry You guys got it right!
@WillWorkForChocolate All of the hackers I know see that as a comedy. Thing is, how much of the geek humor do you get? For instance, why did Eugene “The Plague” Belford use the psuedonym “Mr. Babbage” near the end? That is a simple one… for a hacker.
@john65pennington There is a difference between “nothing better to do” and “likes to do stuff that is enjoyable”. To some, solving puzzles is as good as (if not better than) sex; it trips the same pleasure centers in the brain. If you have ever taken pride in a job well done, I am sure you can understand that.