The problem here is not that they can't obtain a development certificate. The problem is that you cannot use a development certificate to distribute an app on TestFlight or the App Store to other people.
There are two types of certificate – development certificates, which allow get-task-allow for debugging purposes and can be installed directly to a device; and distribution certificates, which do not allow get-task-allow and can be distributed through ad-hoc means, Test Flight, or the App Store.
If this app requires get-task-allow, then it needs to be signed with a development certificate to run. If it's signed with a development certificate, then it can't be distributed to other people.
There are two types of certificate – development certificates, which allow get-task-allow for debugging purposes and can be installed directly to a device; and distribution certificates, which do not allow get-task-allow and can be distributed through ad-hoc means, Test Flight, or the App Store.
If this app requires get-task-allow, then it needs to be signed with a development certificate to run. If it's signed with a development certificate, then it can't be distributed to other people.