It’s because they’ve learned that they can say no and you’ll keep coming up with more options. They’ve exited the game because you created the exit by failing to enforce the boundary.
Yeah I've experienced this when I was young.
My mom was running a daycare at home, and I would sometimes try to help at lunchtime.
Me: <Kid's name>, do you want apple juice? No. Do you want orange juice? No. Do you want grape juice? No. Well that's all we've got, which one do you prefer? None, I want something else. ... and obviously whatever we had would not do.
My mom who saw I was not efficient enough: Okay <kid's name> do you want apple or orange juice? Orange.
My first reaction was "but I already suggested it", but I got better after a while.
