Same reason as they told them about the cure as opposed to just letting them die. Interlude are humans- ironically, they're not the monsters here. I'm thinking that some of Interlude were exposed to the infection as well, and want the cure to be brought back. That, or they want proof of their work. And the characters grew up in Interlude's world, they would probably have a distorted view of Interlude. For instance, Alexis probably wouldn't particularly mind having to scan her card, because she sees her abilities as a blessing. She's not dying, and while she would hold some resentment, she's not going to make their job harder.
Also, on a simpler basis- scanning the card could disable some sort of security mechanism. Like going through a checkout at today's supermarkets.