Agree with it or not, it was a very intentional decision early in the crafting of the html standard that paragraphs have a blank line between them. The <p> tag creates them automatically.
Meanwhile in print just about everything uses the rule we learned in school, a new paragraph gets an indent, not a blank line.
There are ways to recreate this in html, for instance a combination of <br> tags and non-breaking spaces, or more recently CSS can be used to do it.
However, most sites including literotica stick to doing it the way the html creators intended: plain old <p> tags.
I always write with indents and then use find-replace to convert indents to blank lines and actual blank lines (indicating a scene change within a chapter) to a horizontal line (I tend to just use a row of hyphens).