> All that stuff has to react rapidly
Just to add color ... equipment that has to do a lot of work quickly, even if intermittently, has a huge draw. Like your well pump or air conditioner when it starts up.
Now imagine you need to start a few dozen air conditioners simultaneously. The startup energy can be 10x the operating energy.
I've been doing the math on some of this for home solar. In my case I can ramp up the voltage over a few seconds but AIUI rockets still need instant action in many cases.
It's possible future reusable spacecraft could be more proactive, lowering costs and necessary chassis strength. Most of our technology starts off brute force and gets refined with more elegance but also more complexity over time. We're still early days in spaceflight.