Why does :new create a split? What is the use case for that functionality?
Normally when I open a new scratch buffer, I don't want it to be in a split.
:new creates a new buffer in a new window (aka split). From
Create a new window and start editing an empty file in it.
:enew might be more appropriate if you just want a new/scratch buffer in the current window.
For more help see:
:h :new :h window :h :enew