Rereading A Game of Thrones it kind of surprises me that there were no Northerners at all in the Hand’s Tourney except for Eddard’s guards. Not even Manderlys and White Harbor knights when they follow the Seven and practice knighthood. Do you suppose this is due to the Manderlys adopting the Northern disinterest in tourneys? In fact besides Ned’s household I don’t recall seeing any Northerners in King’s Landing or anywhere in the south before the war. The North seem detached from Westeros.

First, about jousting in general. According to WOIAF:

“As knighthood is rare in the North, the knightly tourney and its pageantry and chivalry are as rare as hen’s teeth beyond the Neck. Northmen fight ahorse with war lances but seldom tilt for sport, preferring mêlées that are only just this side of battles. There are accounts of contests that have lasted half a day and left fields trampled and villages half–torn down. Serious injuries are common in such a mêlée, and deaths are not unheard of. In the great mêlée at Last Hearth in 170 AC, it is said that no fewer than eighteen men died, and half again that number were sorely maimed before the day was done.”

In other words, Northmen don’t joust (much – Brandon Stark didn’t do too bad at Harrenhal, there’s Jorah Mormont at Lannisport) because they consider it too refined, too sanitized, too fancy, and boring to boot, whereas southerners consider Northern melees to be disorganized, disorderly, and insanely violent. It’s a nice continuation of the North/South cultural divide. 

Second, about the Hand’s Tourney. The makeup of tourneys depends very much on the location and publicity of the event, and in this case the Hand’s Tourney was A. located down in the South, which means folks oop North are going to hear about it much later and have a hard time getting there, and B. a spur-of-the-moment decision of Robert’s, so there wasn’t the time to get the word out as much as there was for the Tourney at Harrenhal, for example. (Notably, in that latter tournament, the Starks were there in force, they brought their bannermen and companions, so there were way more Northerners)