I am busy doing something else
I am pyrophobic
I secretly hate you (though I still read your LiveJournal)
I am far away, making the trip impractical
I am in the future, making the trip even more impractical
I am concerned that you will keep saying things like "I saw something like this at Burning Man. Of course, that one was twice as big, ten times as dangerous, and the flames formed faces which explained to me the secrets of the universe."