Half the excitement for some of the Marvel releases seems like they could have literally announced anything and a subset of people would be excited for it. It's like... where was the excitement before? I've never heard people clamoring for these characters but apparently they're popular (except when it actually comes to book sales... or having a reason to talk about them.)
The creative teams. If I'm a fan of their previous work I'll likely follow them to whatever book they're announced to be working on even if they feature characters I've not read about before.