It’s usually done so humans are presented as “average”. In my conception, humans are the daredevils. The one thing a human loves more than watching another human do something horribly unsafe is doing something unsafe themselves.
It’s said that the stout and serious dwarves invented the first staircase, but it was a human who came up with the idea of surfing down the staircase on an oaken shield.
Elves have lived in the great Hometree overlooking the Mother River for untold ages. It was a human who first had the idea to jump out of the tree and into the river.
That’s the other thing – dwarves are stout and hardy, but like the stone they came from, once they break, they’re broken. Humans recover impossibly fast by the standards of other races. They’re also the first ones to get up after an explosion or cave-in, with a cheerful “I’m okay!” They can’t take as much as a dwarf, but nobody beats humans at getting back up again and again and again for more punishment.
The Hobbits appreciate Human vigor, their good cheer, and certainly their lusty appetite for food and drink, but the utter glee with which humans will attempt to harm themselves or their fellows in a misguided attempt at “fun” is horrifying. Their rituals and celebration – they let themselves be charged by bulls! – are seen as a testament to human ingenuity, creativity, and utter lack of good sense.
The humans who are most highly regarded by their peers are those who excel at SOMETHING. Dancing, throwing, singing, fighting – humans love watching other humans be excellent at things, even something otherwise pointless and wasteful, like throwing knitting needles into melons.
They are, to a fault, resilient. No Elves would DARE return to a failed settlement. The land is cursed and the dead walk there. Humans will rebuild the same castle over again with the same standing stones.
TL;DR – only humans would invent the X-Games.
Humans are Weird: Fantasy Edition
dwarf: my heart is strong as a mountain
elf: to hear the song of the trees you must cultivate stillness
hobbit: when you get right down to it, there’s no place like home
human: HOLD MY BEER