The problem isn’t just with the editor but also with how your web browser will interpret your html when you switch from the Source mode to Design (WYSIWYG) mode. If the code is considered invalid and cannot be rendered by your web browser then it will be transformed into something that your browser can read.
The issue is that different web browsers such as Edge, FF, Chrome etc. all work differently and may do something different. To standardised this we have something called HTML 5 Standard which our editor must adhere too for cross browser support, so we cannot just turn it off.
HTML 5 Standard definition from wc3
220.127.116.11.2 Flow content
Most elements that are used in the body of documents and applications are categorized as flow content.
a abbr address area (if it is a descendant of a map element) article aside audio b bdi bdo blockquote br button canvas cite code command datalist del details dfn div dl em embed fieldset figure footer form h1 h2 h3 h4 h5 h6 header hgroup hr i iframe img input ins kbd keygen label map mark math menu meter nav noscript object ol output p pre progress q ruby s samp script section select small span strong style (if the scoped attribute is present) sub sup svg table textarea time u ul var video wbr Text
As a general rule, elements whose content model allows any flow content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, del elements and their descendants must not be counted as contributing to the ancestors of the del element.
This requirement is not a hard requirement, however, as there are many cases where an element can be empty legitimately, for example when it is used as a placeholder which will later be filled in by a script, or when the element is part of a template and would on most pages be filled in but on some pages is not relevant.
Often the problem is that the html tag is empty. The only exception our editor currently supports is < i >, < b > and <span> tags as they are now commonly being used for icon fonts. This means that empty tags are not designed to be empty so the HTML is invalid and is treated accordingly. This is breaking the standard and as such there may be consequences which is why we cant really do it.
I hope that helps,