so why not use jets to reach cruise altitude, then switch to ion thrusters ( for which you don't need fuel Because you would need to restart the engines to lan

so why not use jets to reach cruise altitude, then switch to ion thrusters ( for which you don't need fuel Because you would need to restart the engines to land, and that is when they are at a higher risk of failure. You could maybe throttle them right back but keep them ticking over.