I think they must use a fairly soft metal that can take an extremely sharp
edge, because the blades arent' meant to last long or be re-used. Unlike the
OP, I have to shave every day, and I use the same blade no more than three or
four times, because my beard is pretty tough (not a boast, in fact it's a real
pain), and the quality of the shave declines markedly after that.
Remember how much shots hurt when you were a kid? It was partly because you
were a kid, of course, but mainly because the needles were re-used, and harder,
and couldn't be as sharp or as thin as the disposable ones they use today. Same
idea applies to razor blades.