In case you are using a browser without JavaScript or have disabled JavaScript, or are using some customizations which the script on the webpage is not compatible with, then using a script to load the images can be bad for accessibility. (There is a legitimate reason to do so, but it is unfortunately used for many cases when it is not a good reason. If the width and height are hard-coded, then when the images should be loaded is possible to implement in the browser, subject to user settings, without needing a script on the web page.)