There are two main reasons why viruses are not considered to be alive:
1. Viruses cannot reproduce on their own: Unlike living organisms, viruses cannot reproduce on their own. They need to infect a host cell and hijack the host cell's machinery in order to replicate themselves. Once they have infected a host cell, they use the cell's energy and resources to create new copies of themselves. However, they do not have the ability to reproduce outside of a host cell.
2. Viruses do not have the ability to carry out metabolic processes: Living organisms carry out metabolic processes, such as respiration and digestion, in order to obtain energy and nutrients. Viruses do not have the ability to carry out these processes on their own. They rely entirely on the host cell to provide them with energy and nutrients. In fact, viruses do not even have the necessary machinery to carry out these processes. They lack the organelles, such as mitochondria, that are responsible for energy production in living cells.