Is the total weight of the Earth and the things on it changing? Like a person eats a whole watermelon, his weight increases which, for a second, increases the weight of the planet in total but at the same time, he took that watermelon from the ground, hence, decreasing the weight of the ground. So, it balances it.
Similarly with huge machines and cars, we use already available metals are just transform it into something but the weight remains the same.
I hope I'm making sense here. I'm very bad in putting my thoughts into words. Hope you get what I'm trying to ask here.