Boys and Messes

Boys and messes...I know, I know there are probably thousands of entries on numerous blogs about boys and their messes. But what I want to know is why they do it. Do they just think someone else will clean it up? Do they just not care if they live in filth? What could the answer be?
As the mother of 2 boys, 12 and 13, I find that messes come pretty often. Take, for example, this afternoon. I decided to run some errands leaving the boys, as well as two of their friends (I realize that this may have been my first mistake), at home alone. After being gone for awhile I called home to check on them. They said they were making smoothies. Hmm.... I asked what they were making them with, to which they answered "stuff." This immediately made me suspicious. "Stuff" can be anything. I cheerfully said, "Well, just make sure you clean up after yourselves." When I returned home 20 minutes later, my kitchen was not as I had left it earlier. It wasn't as bad as it could have been, but nonetheless I unleashed the fury. The sugar canister was on the counter, along with a lot of stray sugar crystals. The base of the blender was on the counter with some unidentified substance covering it. Dirty glasses and straws accompanied this mess. A big, sticky mess on the floor...which I found out was whatever they had blended and then spilt. They "tried" to wipe this up using every dishtowel in my drawer. Did I mention this mess was dripping off of the dishwasher and cabinets? And this was "cleaned up" to them. Hmmm...
I don't know. Maybe boys just don't think!
Of course they lived and I still love them... At least they tried to clean it up! And I would lots rather them be in my kitchen making a mess than out getting into trouble.