Villain Decay.
They need to give the franchise a rest for about 5-10 years and then return with a new cast. The Future War would be a good place to start (as long as it's night-time and not like Salavation.
Villain Decay, and Power Creep. In 1984 most of the damage on the T-800 (before the tanker explosion de-skinned him) came from one hard crash in a police car and then getting run down by a semi. In later movies the T-800s were getting bounced around on the highway & dragged through buildings with barely a scratch.
The franchise does need 5-10 years of rest. But by then the world will be in such a different place that it's impossible to guess how 'Terminator' will even fit into it. Right now AI advancement is snowballing. Real lethal combat drones are taking over in wars. Hollywood is collapsing from multiple converging factors. In the 2030s there may be little or nothing still valid in T1, and no movie industry left to reboot it even if there was.
The only thing in 'Terminator' that I'm sure will be valid in a decade is the concept of a killer robot attacking people. But that is not exclusive to the franchise. That goes back centuries.