Because people in North America don't have as good a sense of humour when it comes to advertising.Why can we not get these brilliant ads here, although funnily you do get the odd clown who barges past and makes comments about real photographer or such like.
I feel it is quite the opposite. This ad has an "american" feel to me. Not because of humour. In EU...well, Croatia to be frank, standard ads are more in line of "Here is our product, it is great because of this, this and this." Inside joke/mascot/recognizable character here and there, with occasional twist but that's it. There is absolutely no mentions of a competitor and sayings such as "product X from competitor is lame, our product is better because of this, this and this" which seem to me is quite prevalent in the states (not saying all countries in the northern america are the same, as i see you're from Canada, but the majority of ads i see is coming from 'murica).Because people in North America don't have as good a sense of humour when it comes to advertising.
Europe and the Eastern Bloc have always had "funnier" advertising. For us here, it's all very serious and mostly bland. ;-)
Look at some of the English advertising campaigns over the years, brilliantly funny, but oh so subtle in their choice of humour!