Maybe I'm old fashioned but half time is to go to the toilet (optional whether to piss in it or drink from it, maybe both). If you want to see a singer, buy a ticket to their concert.
Don't know how much more exposure you get, especially on a global stage for people to tune in to see rugby league because some famous singer performs 3 songs at half time. Locally, even casual or even non fans would know when the GF is on, no need to spend thousands if not millions to bring a singer. They can just have a couple of LU posters from the opposing teams recapping first half highlights and the match day thread and it would be better viewing.