[Sohcahtoa82]

On one hand, they're nice in that the exact value of your "points" is known and guaranteed.

On the other hand, the conversion often isn't that great, typically 1-3%. Meanwhile, earning rewards in "points" or "miles" can return value in the 5-10% range if you're savvy enough. The savings can be worth it, but some might just use a cash card out of principle (refusing to allow the card issuer to dictate how points are used) or laziness (Just don't feel like optimizing the return).

For me, I use a cash card out of laziness.