Most editors have Enter=New Paragraph as default behaviour.
With Shift+Enter= New Line in same Paragraph.
This is true in MarkText, Typora, Scrivener, word processors, Focus Writer etc etc. Even Vivaldi’s little note editor.
Currently a substantial proportion of users are using or looking for workarounds, which are all higher friction.
Some looking for CSS, some Entering twice, some bulk converting, some using other programs.
New users arriving since Live Preview are even more likely to expect this.
Make Enter=New Paragraph the default with Shift+Enter for new line in same paragraph.
Toggle for current behaviour.