(read the other replies first, I'm going to assume you understand that first!)

There are a lot of researchers writing papers. In many fields it isn't possible to read them all, so you need someone to make a selection of what is useful. Get into Nature any "everyone" will read your paper because it is important. However if you fail that you only get into a small niche publication - the only people who will read your paper are people who search it out - likely because they are in that tiny niche (and have personally met you to discuss this niche at a conference). There are even lower grades up publications which nobody reads, but in theory someone could find it in a search.

What physics papers should a chemist read? If you are a physicist you should be reading more papers, but there are still too many to read them all so you need a selection, but that selection should bias to others working on similar problems to you. The same applies for every other field: you can't know everything so you need someone to apply a selection to tell you what is important for you to know.