Why no scientists insist viruses are not alive?

Whether or not something reproduces is a factor in determining life, but it's not the only one. Crystals, for example, will form on their own and nucleate new crystal formation, but they're not alive. Viruses aren't alive because they can't replicate on their own, and have none of their own internal processes - they need to hijack a host cell.

You could draw a parallel to human DNA. You can take DNA out of a cell and store it in a tube, and later re-insert it into a new cell - the DNA is required, but it isn't alive on its own.

Another way to look at it is to think of a vial containing water, nutrients, and a sample of virus. You can let the vial sit there for a long time, but in the end, all you'll ever have is what you started with, because the viruses have no processes of their own. A sample of water, nutrients, and bacteria, though, will break down the nutrients, replicate, and excrete waste products because they are alive.

Virus's are often described as being on the edge of life, this is because life is defined as requiring organisms to be able to independently reproduce. Viruses do not do this, hijacking the machinery of a host cell in order to reproduce.

viruses can "die" for many years and then come back to life spontaneously... that is just one sorta big reason. Scientists believe that things that are alive just don't die and then like ten years later spontaneously come back to life

Viruses can die for many years and then come back to life spontaneously.