The Store application version requires a minimum ServiceNow family release that is newer than your current instance version (e.g., app requires Utah but instance is on Tokyo). (high likelihood)
The application version you're trying to install has not been certified or tested for your current ServiceNow family release. (high likelihood)
Your instance family release information is outdated or incorrectly cached, causing the Store to misidentify your version compatibility. (medium likelihood)
The application has been deprecated or withdrawn from support for your current family release by the vendor. (medium likelihood)
There's a temporary synchronization issue between the ServiceNow Store and your instance's release information. (low likelihood)