The
ZO_ScrollingSavingEditBox is a highly complex object that combines several controls and uses lua code to achieve the behavior you see with the MotD. You cannot replicate it just by letting an edit box control inherit its template. Instead you'd have to use it as seen in the code for the guild MotD.
I'd also recommend you look at the source code extract on github, since UESP doesn't seem to include the xml files.