Three words as to why:

Slow.

News.

Cycle.

I'm surprised about the repercussions of this effect.  I expected newspapers across the world to start posting caricatures of that figure to demoralize the enemy,  yet somehow the comics have not gotten onto the web.

Well, it would be intuitive to think that those who violently opposed the media would dislike the idea of the icon they wanted to supress plastered around the internet.

The reason why this row didn't happen when the cartoons first came out is because of one highly significant factor that hasn't been highly publicised.  After there was an initial protest by the Danish muslim community there was a reconciliation and things died down there.  Then, a group of extremist Danish imams who were disappointed that it hadn't been a springboard for extremism went to the International Muslim Council (forgive me if I've misremembered the name of the body) and showed these drawings to them. 

That would have been bad enough, but they ALSO took along a bunch of other drawings that were EVEN WORSE.  These included drawings of the prophet Mohammed with the head of a pig, the prophet Mohammed shagging animals and the prophet Mohammed as a paedophile.  I'm not sure who drew these pictures or if they made them themselves to stir things up, but they were NEVER printed in the Danish press, and I'm sure cartoons that went THAT far would have caused the Danish government to put the newspaper editors in prison as they obviously went a lot further than pictures of Mohammed with a bomb in his turban.

Anyway, to cut a long story short, THAT seems to be the reason for these cartoons sparking riots and burning down embassies etc. which is a bit more understandable if Muslims in the Middle East believed that cartoons of their holy leader as a paedophile were being printed (and reprinted) in European newspapers and then being defended as a freedom of speech issue.  You wouldn't ever have cartoons of Jesus as a paedophile in newspapers even though people make fun of Christianity all the time (and even with all the stories of those Catholic priests abusing children). 

So it seems to be a combination of extremist imams in Denmark taking things to the next level after failing to stir things up in Denmark and a misrepresentation of things to Muslims in the Middle East where there were also extremist factions who saw this as an opportunity to vent widespread public opinion through violence.

P.S.  Nevertheless, Denmark is the only country in the world where there is an actual Nazi party that is actually allowed to exist and take part in elections etc. so who (if anyone) has got it right?