I’m not a developer, so i can’t say why. Probably at some point, when Java 5 and 6 were still mainstream, support for this versions was ‘hardcoded’ into Spark’s code and now when Java 5/6 is not available on the system issues popup.
install4j is in development (latest version released two days ago http://www.ej-technologies.com/download/install4j/changelog.html), but i’m not sure latest version is in use in Bamboo (which produces installers) http://bamboo.igniterealtime.org There are no fulltime devlopers or maintainers here, so some stuff gets old. Though Jira and Bamboo got updated to the latest version recently. Will ask another community member about the situation with install4j. Ej-technologies has granted a free license to use install4j on this site and for the developers a few years ago (http://community.igniterealtime.org/blogs/ignite/2011/09/03/ej-technology-grants -install4j-license-to-the-spark-community), but i don’t know if this covers all the new versions.
Also, i’m not sure the problem is with the installer. It is probably somewhere on the Spark’s side or in the configuration of the installer or Bamboo, which puts the hooks to search for Java 5/6. Someone with a good Spark’s source and installer configuration knowledge should look into this and find a solution, but as i said, we lack such experts here. If you search the forums, you will find other people using launch4j, izpack, advanced installer and other tools to produce their own installers, but they don’t tie in so nicely into Bamboo system as far as i know. And izpack installers are a bit cluncky from my personal experience.