Traditionally, web applications worked by sending an entire generated page of HTML to the user, waiting for the user to perform some action, such as a click, and replying with another entire generated page of HTML.
If all that you wanted to do was to delete a single row in a table of hundreds, then it does not make sense to spend time regenerating the hundreds of other rows (database strain), importing and parsing your web templates all over again (hard drive, CPU, and RAM strain), and asking the client to download external resources, such as ads (bandwidth, network lag), all so that you can delete a measly hundred bytes.
The blogging software WordPress is an example of how it should be done. In the control panel for WordPress, whenever a comment is marked as spam or deleted, the comment simply vanishes from the page. The page does not reload.
Unfortunately, most software applications out there are written with just PHP and HTML, and the smallest amount of client-side JavaScript...