Why should footnotes be avoided in scientific publications (natural science)?
If you don't stop/discourage researchers from adding footnotes, you will end up with articles with huge amounts of footnotes. As you are doing research you will learn a lot about a specific topic, and most of that will not end up in the final article. The temptation is to add that to footnotes. However, a good article is one that has a very specific aim and does only that. So you should resist that temptation. Such rules are there to help you.