It's a minimum of 1 cent per mile because you can get miles converted into cash/gift cards in a number of ways.
But that's a bad use of miles.
If you don't adhere to Ts and Cs and "sell" your mile you should get 2c/mile on the gray market. So there's an independent valuation of a market where some people are willing to pay that much, and others are willing to sell for that little. The fact that there is some risk to the transactions undoubtedly has an effect on the supply and demand.

Domestic, coach fares, I would use them if it's a minimum of 2c/mile.
But where I most use them is in redeeming for international fares, where it can go up to 10c/mile.
However, keep in mind that I would never pay $15K for an F ticket to Singapore, so this is a phantom value.
It's like the "free minibar" that I get as an IC Royal Ambassador. Sure, it's nice to say that I got $75 in "value" by taking 5 drinks and some Perrier out of the minibar -- but reality is that I would never have spent that much -- to me, it's "worth" $15 at best.