It's what you're used to.  I used to go watch speedway every week, and never thought twice about the smell.  Now I need a hit of it every year or so!
There used to be an element of 'underdog' with four strokes, as they were mostly glorified enduro bikes for a while.  People would automatically gravitate towards them if they were in a race, just because they were different; and especially if they were doing well.  
The Thumper Nats was interesting, because we got to see whole grids of these weird & wacky bikes, with pro motocrossers well out of their comfort zones riding these big bad hunks of metal.  I had the opportunity of riding Stefan Merriman's TT600 Belgarda thumper nats bike for a day in '97.  That thing was tuned off its head.  I don't think I've ever ridden something so powerful.  That was all great until you tried to jump the thing or make a tight turn.  You could turn the QE2 quicker!  A real challenge for the rider.
When the purpose built YZ400F came along, it basically killed the concept stone dead.  It wasn't a modified trail or enduro bike.  It was built to destroy 250 2-stroke motocrossers!
Now we've gone full circle, and we find the two stroke guy the underdog, and a lot of people are totally over the farty four stroke sound we have today....  
