Stefan Judis explains why developers should be a bit responsible when it comes to setting HTTP Headers of web applications. Having proper HTTP Headers like Cache-Control will be a deciding factor sometimes if the web application is accessible to some people or not.
If a page on a hospital site is 5MB it is not only slow but also could be too expensive for people needing it the most. The price of 5MB in Europe or the United States is nothing compared to the price of 5MB of data in Africa. Developers are responsible for keeping the web affordable for everybody. This responsibility includes serving the right resources, evaluation of the right tools to use (do you really need a JS framework for a landing page?), and avoiding requests.