Enabling/Disabling of Marketing Automation button is handled from the app dependency section under Sitecore.Marketing.Automation.Client.config as below.
<appDependencies>
<marketingAutomation dependencyEvaluator="Sitecore.Marketing.Automation.Client.DependencyEvaluator, Sitecore.Marketing.Automation.Client">
<!--Hides MA application button from Sitecore launchpad in case if XDB is disabled.-->
<app id="{3A86E677-5AD1-4315-B7B5-EFA11988119A}" name="Marketing Automation" />
</marketingAutomation>
</appDependencies>
Check inside above class contains 2 conditions.
- XDB is Enabled
- License file has the module Sitecore.Automation
Since you have already enabled XDB, can you check if the license file contains module 'Sitecore.Automation'.
Hope this helps!!!