To get to the other side? Because it felt like it? To create a talking point? Because it wanted to be remembered it one of the most well-known (if one of the least funny) jokes in the world?
The point is, no one really knows why the chicken crossed the road, but no one seems to be able to let it lie - there has to be a reason. Just like there has to be a reason behind every design decision you'll ever make. This has become painfully obvious in my time studying Graphic Design at Leeds Uni, I can no longer just design something 'because it looks good' like I did in my A-level Art and Photography days. No, my decision to place this photo in that corner and that piece of text in the other has to be well thought out and easily explained should the question of 'why?' ever arise...
Of course, there are parts of my work which are designed because they simply look good, but after years of practice, be it at school to teachers explaining why my coursework is late AGAIN or at home to the rents who are enquiring why their new vase (broken whilst playing a 'friendly' game of football with the brothers) is now residing in the rubbish bin in several different pieces, my ability to 'Blag' my way out of these situations has become particularly noteworthy.
It has to be said, whilst it may not be looked upon particularly kindly, the ability to 'Blag' will serve anyone well, not just in design but in life in general. How do you think that guy who will quite possibly end up working next to you ends up earning more than you, despite being noticeably less proficient at his job and having been at the company less time than you? He's a damn good blagger.
So the next time you do something you can't really explain, and the inevitable question of 'why?' is asked, make sure you know how to blag it.
(By the way, I reckon the chicken just felt like it.)