If there was no target="..." for external links, then clicking such a link would immediately
exit the TiddlyWiki you are viewing (unless you had unsaved changes). This would discard
whatever context existed (e.g. currently opened tiddlers, search keywords,
and any $:/state/... tiddlers). I suppose there might be a use-case where that would be
appropriate, but in general it seems like it shouldn't do this by default.
I suppose it could be useful to extend the "[ext[...]]" syntax to permit specification of
a target, i.e., "[ext target=... [...]]". If this was added, then you could write
"[ext target=_self [...]]" to force a link to open in the same tab/window.
However, if you really want an external link to open in the same tab/window,
then you can already use standard HTML syntax, which is simple enough:
<a href="../20200703224247/index.html">Open file</a>
Perhaps if you explain your use-case a bit more, it might shed some light
on why you want this behavior in the first place.
-e