I'm adding an answer from softaculous support team:
"
In WordPress Sets(when installed) Plugins are activated by default but the theme was not activated. We have fixed this in Softaculous ver. 5.6.4 and if the set has only one theme that theme will be activated. If there is more than one theme then no theme will be activated.
Softaculous 5.6.4 will be released in a few days and then this option will be available.
"