Incubator was actually cranked up slightly before Beta Wikiversity.
https://incubator.wikimedia.org/w/index.php?oldid=1 02:23, 2 June 2006
https://beta.wikiversity.org/w/index.php?oldid=1 08:59, 15 August 2006
Wikisource is 2,5 years older https://wikisource.org/w/index.php?oldid=3 00:51, 24 November 2003
The more precise answer for having Beta Wikiversity from its supporters typically is: "Wikiversity is different project than other wikis so it needs its own site."