The majority of folks in this world live on much, much less than us fortunate ones. These, and the majority of DE blades, are for them.
I was visiting my wife's family in Vietnam last year. I was wandering the shops, close to their house, and found a bunch of DE blades. Bic, Gillette, Krona etc. They were very inexpensive. Around $6 CAD for 100. Beside them, they had some Mach 3. Aorund $5 for three. I bought a couple hundred of the DE's and a pack of the Mach 3's (travelling... no time, that sort of thing).
They could not believe that I would spend that kind of money on the Mach 3's. For some perspective, a very good wage in Vietnam, is around $300.00 per month.
TEFL.com has a useful section which lists the price of many items in hundreds of cities in the world. Didn't check grooming supplies, but after the initial shock of cheapness, it's tempting to change "how can things be so cheap here?" to "why are things so expensive at home?"