This is due a strange deal by PIONEER and the companies Sony. Pioneer holds all rights on that video, and it disallows any releases on further formats. You can read that on wikipedia if you search for LaserDisc.
Anyway, there is 1 exception: A Genesis DVD has been released in 2002. That was maybe because the band did not exist during that time. A fact might be, that it is all about money, and maybe Pioneer does not want to pay anything to the artist for a re-release. So we do not get a DVD.
We have started a big campaign, and I hope you join us on facebook:
tinyurl.com/paul-simon-campaign
facebook.com/pages/Campaign-for-the-1991-Paul-Simon-Concert-in-the-Park-to-be-released-on-DVD/248186498533473
Please join us, like this page! We need thousands of votes!