I imagine there are several possible answers to the above questions; however, I believe the following has to be in the top three. They simply don't understand the complexity and fragility of the ecosphere. They just don't get it. They grew up in a world of relative abundance in natural resources, and a population less than half of today's world population. They seem to be stuck in the Past.
In addition, most politicians and their advisors cling to the idea of perpetually unlimited economic growth. They believe any damage from such will be mitigated or eliminated by Technology. So, full steam ahead!
To illustrate the interactions and connections they're missing - concepts which must be understood if we are to avoid the collapse of organized human existence - today I created the following diagram. [The title is Complexity Connections.] It harkens back to Barry Commoner's First Law of Ecology in 1971: Everything is connected to everything else.