Perhaps its because of changes to the l.b.w rule that hat tricks are a little more common, that, and more international cricket is played and finally there is a lot more one day cricket, which changes batting strategy dramatically and doubtless leads to more batsmen taking more risks to keep up with the required run rate.
Maybe originally it was the umpire that had to provide the hat? Now the umps are provided with hats and they tend to fire them out for LBWs just for the publicity. 
“What price Brett Lee getting the next one?” Name your odds… when was the last time you saw him bowl three wicket taking deliveries (as distinct from scalps) in a row?