I tried copying and pasting this, and it does not show the result in
plain text (bold, for instance, displays fine). I think what you're observing is that the transclusion is displaying in
inline mode, which means that things like section headers and paragraph breaks won't show up.
To get it into block mode instead, put a blank line before and after {{!!text}}. Another option is to use the $transclude widget instead of {{!!text}}, which lets you explicitly specify whether you want it in block or inline mode: