Why are landfills sites bad?

landfill sites can be very harmful to the environment because most off the waste left on these sites is unrecycleable and as a lot of food these days has a lot of preservatives in and packaging is more oftne than not plastic, these dont naturally bio-degrade for hundreds of years. This is very messy,as the garbage is not contained, smelly, as it smells of rotting waste, pollutive, and very bad for soils and wildlife around the landfill site.