Keep and Reader are built for different groups of users. Reader was a niche product used by a small (but vocal) subset of all Google users. Keep is a product built for everyone.
Reader.. not so much.
How so? Show me someone's blog subscriptions, and then metrics on entries they clicked on, how long they viewed it, and the clicks that they followed, and I could quickly get a very accurate profile of the person.
I suspect there will be a lot more than just todo lists, so the possibilities are really endless.