Why is removing presentation-oriented markup from one's html document considered to be a best practice?

Answer

Its for the purpose of  maintenance and readability

Explanation

A presentation-oriented markup web application generates interactive web pages containing various types of markup language.

Markup is a language designed for the purposes of processing definition and presentation. It specifies code for formatting, both the layout and style, within a text file. Markup describes the structure while the styling is how it looks. it uses the code to specify the formatting which are called tags.

you can only change it if your real name or personal information was in it. and if so you would need to contact them directly with a username change request.

answer; wireshark;