Do we need to sterilize the jars before putting the food in, and why?

In a lot of guides on how to do canning, they say to sterilize the jars before putting the food in (for example https://morningchores.com/how-to-can-food/). I don't understand the rationale. The jars and all their contents will be fully sterilized later when doing the final sterilization. What is the problem or danger if some contamination is there before the final step? Nonetheless that there will be contamination anyway coming from the exposure to the air.