Among other things, DC can redeem to a variety of hotel programs. If SPG meets all your hotel needs, that's fine. I needed Best Western points (or else pay through the roof in peak season) for a stay outside Bryce Canyon National Park, and found that Diners Club could get me enough points for several nights with relatively few DC points.

I've got enough ways to collect miles into the "mainline" airlines, I want an even more fleixble card (multiple airlines, including ones I may only ever use once like Icelandair, and multiple hotel and motel programs).

Then there's the "always, alwaya, always primary" rental car collision coverage. Some people keep the card for that and that only.

Finally, many people get 10k "retntion" bonus almost every year. That more than pays for the annual fee if you make good use of those 10K points. (10k DC points certainly piad for more than one night of that $150++ BW stay.)

If all you use your card for then, is one or more ailrines that SPG transfer 1:1.25, then maybe it's best for you. But if you want a card that transfers to a variety of hotels, there are several options (DC, AMEX MR, maybe someday Sapphire*?), but SPG isn't among them.

(And I've found that, at least on domestic trips, depending on the destination, I need points help with hotel stays much more than airline fares, and surprisingly often enough in "rural" situations where the "big" hotel brands don't even have a presence.)

*You would think that Sapphire should be able to transfer to all the hotel programs that Chase has cards for, but then you'd also think that Sapphire should be able to transfer to all the airline programs that Chase has cards for...