Self Service currently only shows what apps are scoped for a device. If you have expensive apps that not everyone needs you scope it to those who have requested the app. This leaves other employees unable to see the apps and confused why they don't show up in their self service.
Remedy: Allow all apps that are specified to show up in Self Service. If the app is not scoped for their device instead of Install it would show a Request button. That will blast off an email with the device name, user name, and app request to an email address or ticket system.
Bonus Points: In Jamf there are Notification Tabs on devices - I can visit a request section click approve and authorize the device. If there is not enough licenses it shows me a link to the VPP website. I Click, buy a license, then refresh and click approve. Boom!