Why are biogeochemical cycles important to ecosystems?
because matter on earth is limited in amount, and space for dead bodies as well.
If dead bodies accumulate on earth, then there will b no space to keep all of them. This is one reason why recycling their bodies is important.
Another point is that mater is found on earth and has been there since earth was developed and became ready to support life. After that matter has not been added to earth in big amount, nor in a regular manner, so it must be recycled to support the new organisms which are continuously being added to the ecosystem.