ISPs are organised in a hierarchy where the Tier 3 ISPs are connected to Tier 2, and Tier 2 ISPs are connected to Tier 1 ISPs. Why are they organised in a hierarchy? Is it because if all devices were connected directly to each other, then the structure doesn't scale and becomes inefficient?
PS - I wasn't sure on which stack website to post this question, and this seemed like the best fit. However, if there is a website where this would be a better fit, please comment.