Why take the case ? Hear the case at the court , make us wait a few months?
I'm not a lawyer, but my observation is that who has standing may be simple to decide in most cases, but in others turns legitimately on fundamental issues that need to be fought over.
For example, I think there are quite a few cases that need to be brought that will turn on who has standing--and the fulcrum will be the separation of powers defined in the Constitution. How many times over the past hundred or more years has the FedGov stuck its nose where it simply has no right to be a party in the dispute? Where the Constitution says, "Congress shall make no law . . ." and Congress has? Or even stupider, where some Federal judge or Justice has a feeling about something and wants to make it into law?
It's a battle that will have to be argued and won.