Sorry it is late.
I once heard that shaving with cold water extends the life of a blade. I never followed that advice until this summer. I started using cold water a couple months ago and it seemed to work. The first cartridge I used it on lasted weeks longer than usual. So long that the lubricating strip had mostly worn off.
Any idea why this works?
Or time and repetition. Sure, sediment in water erodes rocks, but some of the erosion is dissolution or wear from the water itself. A softer material can abrade a harder one - for a simpler example, rubbing a sharp bit of copper on a flat piece of steel will scratch the steel, even though the copper is softer (the copper comes off worse, of course, but so do the beard hairs in the OP)
Part of this may be due to the fact that you get a better shave with cold water than hot, so your perception may be colored by this.
Not to dispute anything that has previously been posted but I would like to add this:
These blades are extremely thin and they are very sharp. That is due to taking a thin piece of steel and honing it to to a thinner edge.
I once worked in a lab and had to hone microtome blades. These were used to cut extremely thin cell samples. What we did was examine the edge of the blade under a 500x microscope. The edge of a blade that was “dull” looked like the Himalayas. It would be put on a honer for hours. When it was sufficiently honed the edge looked perfectly straight.
Razor blades are thin and extremely sharp when the leave the factory. It is not that difficult to, over time, dull them due to a variety factors that were pointed out earlier. Yes, if you could put them on a honing machine you could restore them. Of course, that is pretty much impractical. So, they sell you new ones.
Our microtome blades would “dull” doing work with cells that were hardly as sharp as the steel they were made of. Still, we would have to maintain them. Corrosion, the edge bending, whatever. I hate to think what a “sharp” kitchen knife would look like under a 500x microscope. That’s the physical world.
Do you have hair on your face?
Those dollar store things dont even touch my facial hair unless you count ripping snagging and pulling.
I get many months of use out of one disposable twin-blade (for trimming around the beard).
Sort of like Winston Smith in 1984. 
I’m still using the razor I bought in 2012, of course, I use a straight razor and I’ll probably die using the same blade.
That could be read more than one way. :eek:
My thought, too.
LOL. I wish that had been intentional