There are lots of great thought below. I race in Rocky Mountian Masters and when it has just dumped 12 like this weekend and there is 15 of you in speed suits, and you are going up the lift and you see great lines being laid down in the trees.
The other reason is there are few of us old guys willing to put it on the line, sacrifice, train, perfect even the smallest of imperfections to finish : off the podium . So for me I love the competition. I guess you can measure a great run with out a clock but is very easy to measure a great run with a clock!