The multiple character approach for sublists was the first wiki syntax for sublists. Users do not need to count leading spaces like in markups where a sublist level is determined by the number of its leading spaces.
Ignoring the indentation makes at least the first-level (most common) lists work across practically all wiki engines that use asterisks for lists, and is also friendly for users who indent their lists reflexively.
Multi-line and multi-paragraph lists are too rare and complicated to include in core standard.
Starting with Creole 0.6, they are chosen for the following reasons:
Hyphens (-) were not chosen in Creole 0.5 and earlier due to the following reasons:
The number sign (#) is used for ordered lists in most wikis. Using the same rules as for unordered lists makes it easier to learn and remember the markup.
The number was not chosen as it defeats the point of having ordered lists, since you have to number your items anyway. Also, you would have to type two characters instead of just one.
(25) Multiple asterisks: Clearspace, Confluence, ErfurtWiki, IkeWiki, Instiki, JAMWiki, JSPWiki, KWikiKWiki, MediaWiki, miniWiki, Netcipia, Oddmuse, PBWiki, PmWiki, ProjectForum, ProWiki, Socialtext, TiddlyWiki, TikiWiki, UseMod, Wiclear, WikiDoc, Wikispaces, Wikyblog, XWiki
(23) Multiple number signs: Clearspace, Confluence, ErfurtWiki, IkeWiki, Instiki, JAMWiki, JSPWiki, MediaWiki, Netcipia, Oddmuse, PmWiki, ProjectForum, ProntoWiki, ProWiki, Socialtext, TiddlyWiki, TikiWiki, UseMod, Wiclear, WikiDoc, Wikispaces, WikyBlog, wxWikiServer
(2) Indented number: WikiSH, wxWikiServer
(2) Indented hyphen: DokuWiki, Qwik