Why isn't this implemented by default in vim? (line by line Scroll) [closed]

Question

Very often, my preferred way of navigating a file in vim is by "scrolling" line by line. By scrolling, I mean shifting the lines up/down while keeping the cursor on the same line and position. <c-d> and <c-u> implement this already, but they do so for half a page, not one line.

So I made bindings that implement what I need:

noremap K k<c-y> (technically I have noremap K @='k<C-Y>'<CR> to accept a count)

noremap J j<c-e> (technically I have noremap J @="j\<lt>C-E>"<CR> to accept a count)

So hitting j and k move the cursor up/down one line, and J and K scroll up/down one line.

But I've learned that vim bindings are made very intelligently. For example, I was always annoyed that searching using /<term> and ?<term> highlight the term and automatically make the cursor jump to the next/previous occurrence of it. I initially wanted them to just highlight the terms and then optionally choose to jump to them by hitting n, so as not to reset my view if the term doesn't exist in the current view. But I soon found myself using these search methods not necessarily to search for these terms, but to actually jump to them, as a way of fast navigation. I.e. it is sometimes much faster to search and jump to a pattern to navigate to a line position than by manually moving the cursor (using default movements) to the desired position at a line and position, even if that position is currently in view. And if the term doesn't exist in the current view, I can just call <c-o> to reset the view back to where I was.

So is there a reason why line by line scroll isn't implemented by default? I suspect that by making a macro for scrolling, I might be using vim not the way it is intended to be used/not in the most efficient way.

Edit: in terms of the scrolling functionality itself, I think the mappings above implements it fairly well and are convenient to use for my purposes.
Edit1: I just found out that in Tmux copy-mode with vi bindings enabled, i.e. set-window-option -g mode-keys vi, they do implement scrolling the way described above, also using K and J.

Answer 1

                            *CTRL-D*
CTRL-D          Scroll window Downwards in the buffer.  The number of
            lines comes from the 'scroll' option (default: half a
            screen).  <b>If [count] given, first set 'scroll' option
            to [count].</b>  ...

Execute 1<ctrl-d> for one time, it will set 'scroll' to 1, you can then use <c-d> and <c-u> to do line by line scroll without moving cursor.

Answer 2

Most likely the developer didn't feel that this feature is important enough to deserve a simple key. On the other hand it is possible to create mappings using 1<C-d> and 1<C-u> when you need it.

Remember that vi was initially implemented by Billy Joy in 1976. At that time scrolling the screen might have been an expensive operation.