In our modern world of "technologicals" and "internets",people have to be able to move stuff around. When it comes to moving lots of shit (or one shithead), the best vehicle for the job is a truck.
Since, like, forever ago, mankind has been obssessed with reallly big stuff, bigger stuff, and the ever-bigger cheeseburger. (I say mankind, but this really only applies to men) The reason as eplained by science? Boners. Since you can't whip it out and show it to all the subjects in your kingdom, all you have to is build an oblong fuck-off sized tower. Fast foreward to modern day. Sure, you can build huge penis monuments, (Way to go, Egyptians. Same to you, Washington.) But wait! What if you need to prove your penis size in a faraway corner of the country? Miles and miles away? You can't take your monument with you... (unless you are Bruce Lee)
"If you don't need a step ladder to get in, its not worth getting in at all!"