A: I am a troll who traffics in clickbait. RIs are still there, but it's getting eclipsed by better things. Think SimpleDB.
A: Because you weren't in the room with this question when the product was being built.
A: It must suck to be you, because this offering won't help you any more than RIs did.
A. Show me an expensive Lambda bill compared to EC2 and then come talk to me.
A: Surprisingly nothing. It's all net positive.
Spot isn't always a fit either.
True, you can't do that with Savings Plans. But you also couldn't with Convertible RIs, and the secondary market is something of a ghost town. I'd not count on it strategically...