Why doesn't trash decompose in a modern landfill?

Answer 1

The simple answer is that it does! Everything decomposes eventually. Unfortunately, many household, commercial and industrial waste products are made from materials that take an awfully long time to decompose; plastic for example. Some types of plastic can take up to 50,000 years to decompose fully! Other waste items such as tin foil can take upward of 100,000 years! Even with the (comparatively recent) advent of recycling, much of the waste that gets assigned to landfill is, indeed recyclable. This is partly because so many recycling plants are already operating at full capacity, or are governed by strict input / output quotients. Of course, despite what the governments of the world would have us believe, it is often cheaper to export waste to landfill sites abroad than it is to recycle it domestically.