A hatchery wouldn't be interested in a method that kills off male chicks, such as a higher incubation temperature. They're after a method that makes all of the eggs female, or some way to tell the sex of the egg before it's ever placed in an incubator. And either way, it needs to be cost efficient (which isn't easy to do when the "valuable" female chicks are worth a couple dollars each and the males are worth next to nothing).
Hatcheries don't want a method that causes most of the males to die in the shell. They can make more money selling male chicks than they can selling full term unhatched chicks that died in the shell.