The Raptor has outsold the Corvette every year since 2009. Yet, it's still profitable for GM to build those on a bespoke chassis in their own assembly plant, probably sharing the least with the rest of the fleet out of anything. So, you'd figure tweaking a platform they sell almost 1M a year to be a bit better off road and sharing a ton of parts with that same vehicle shouldn't break the bank.
I'm not saying the ZR2 is a bad truck. It looks great and is a solid competitor to the Tremor, Rebel, and TRD Pro. However, it's still not at the level of the Raptor or TRX. There is room in the market for a ZR8 or whatever you want to call a top end halo truck with an LS7. It would get people into the show rooms, if price was a bit out of their budget, they'd go home with a ZR2 or Trail Boss. That's how halo vehicles work.