Because making functional things from something generally thrown out is bad now

It’s more that there are so many humans and so much demand on various resources that there is almost nothing that doesn’t cause some kind of harm even if it provides some kind of good. There’s basically nothing that if scaled up enough won’t cause problems. Petrol aka “gas” used in cars was once thrown into the gutters more or less. We didn’t “invent it” so much as it was there. The origin of model fuels can be found in the creation of lamp oil. Someone finally said: “Hey! This is useless for anything else but we can fuel internal combustion engines like cars pretty well off this stuff....” and centuries later we are trying to phase out or mitigate internal combustion engines and oil dependency due to pollution and dwindling resources.