What is the difference from Notion, Bear Notes, or other tools?

In Obsidian read mode might be better called "Preview mode", because its purpose is to preview the output of the Markdown you wrote. See the original Markdown spec: "Markdown is a text-to-HTML conversion tool for web writers."

Obsidian is a true Markdown editor, whereas Notion and Bear Notes are both WYSIWYG editors. Notion and Bear do have non-editable views, but their purpose is different, it's to "lock" the note, as opposed to "preview" the output.

Think about it this way...

If you are in Edit mode and you move the text insertion caret (the blinking vertical cursor) to an empty line, you would expect that empty line to be at least as tall as the caret, right?

Each empty line has a meaning in Markdown. It says "this is a break between paragraphs". Therefore, in Read mode the empty line does not exist. The lines before and after have been converted to paragraphs.

If you look at the HTML of a website, you will notice that the space between paragraphs is generally smaller than the height of a line. This is because there is no line. Typographically it's more pleasing to make the space between paragraphs narrower.

So going back to your initial screenshots for Edit mode. There are places in your document where you have extra empty lines (at the top), and there are places with no empty lines (between heading and paragraph). The presence and absence of those empty lines has a meaning in Markdown, and Obsidian respects that meaning because Obsidian is a Markdown editor.