You don't need spaces on empty line. This is the reason Vim removes auto-indentation after Esc.
Whenever you're going to write something on empty line with indentation applied, you can press cc or S. Or you can re-indent text after you've finished with it (e.g. == or ='[ and so on).
You have autoindent on:
*'autoindent'* *'ai'* *'noautoindent'* *'noai'*
'autoindent' 'ai' boolean (default off)
local to buffer
Copy indent from current line when starting a new line (typing <CR>
in Insert mode or when using the "o" or "O" command). If you do not
type anything on the new line ...