This is because ACS now has an extra setting to disable dynamic users. If enabled the external users will not be included in the package.cab file. The setting is in the Configure Caching Unknown Users section on the External Authenticators ACS Admin page.
Also worth a mention, on the User Setup page there is the Remove Dynamic Users button, that will do exactly that!
TIP: If you wish to purge stale records - export the cab into aaa-reports! and run the inactivity reports to see which user records can go. Only then should you remove the dynamic users.
SHAMELESS PLUG: csvsync v3.0 can initiate the creation of the package.cab and download it ready for automated import into aaa-reports! enterprise v1.1