To understand why such a large portion of the planet doesn't care about destroying Earth you need to understand a few factors.

• Certain religions say God will always provide for people so it doesn't matter what they do.
• Some people are just so selfish they don't mind burning everything on the way out. This works well with the first factor.
• Most people are so poor and desperate they are just trying to survive and so don't have the luxury to help.
• Some people want to keep the desperate people desperate for their own selfish needs.

So if you find a very rich religious person who uses poor people and does't care about the problems of the next generation then you have essentially found your culprit.