The CreateAccessServicesApp function configures a database server to use with access services, but it does not set the "AvailableForCreate" to $true on that database, so you can't actually create any WebApps from Access 2013.
After creating it, it needs to run the following with an appropriate $serviceContext:
```
Set-SPAccessServicesDatabaseServer -DatabaseServerGroup DEFAULT -DatabaseServer $dbServer -ServiceContext $serviceContext -AvailableForCreate $true
```
After creating it, it needs to run the following with an appropriate $serviceContext:
```
Set-SPAccessServicesDatabaseServer -DatabaseServerGroup DEFAULT -DatabaseServer $dbServer -ServiceContext $serviceContext -AvailableForCreate $true
```