I swear, some locks are designed to fail! Honda, Toyota, Kia... You know you're guilty. If I got into the nitty gritty I would bore you with long rants about pick resistance, or binding order, or manufacturing inconsistencies. But I'll just get to the point instead. Some automotive locks are considered "high security" but really it's just a name. Different manufacturers have explored lots of variations of the tried and true "pin tumbler lock". What some came up with is a lock that is just as easily defeated with force (i.e. Breaking, smashing, drilling, etc.), just as vulnerable to picking (with the proper tools and skills, of course), and far less reliable than some of the worst non high security automotive locks out there. So you ask "why do they do it that way?" well I just don't know. But what I do know is that some of them rely on a very tiny metal peg that sticks out and runs along the length of the key. These pegs wear down over time, especially in your ignition Lock. The key also wears down and eventually the peg goes off the track and the key stops working. This can start as a sticky key that you gotta wiggle to get it to turn, then eventually it stops turning all together. It only takes one tumbler to stop being lifted to make the lock never turn again.

There are other reasons why ignition locks stop turning. Just dirt and grime can play a big part, along with very old and worn out key blades. This happens on car door locks too but far less frequently because most people don't use the door locks with the key, they just use their remote.
Another major reason your key won't work anymore is because of tampering. The usual suspects are kids messing around where they shouldn't be and curiously sticking a foreign object inside of the lock, like maybe a toothpick, Bobby pin, or some other key that doesn't belong there. All these things can easily seize up the lock for good, leaving you stranded, desperate, and unsure of what to do.

Ben the locksmith to the rescue! I'm highly specialized in automotive locks and in most cases can remove, repair, and replace any ignition Lock or door lock cylinders. When it comes to DIY house locks there's not much you can mess up... but servicing car ignition locks improperly can lead to that can of worms you wish you didn't open.