Why convert2rhel failed with "This system has no repositories available through subscriptions."?

Issue

• convert2rhel failed with This system has no repositories available through subscriptions: using activation key created from customer portal

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  Description of problem: This system has no repositories available through subscriptions.
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  DEBUG - Calling command 'subscription-manager repos --disable=*'
  CRITICAL - Repositories were not possible to disable through subscription-manager:
  This system has no repositories available through subscriptions.
  
  DEBUG - Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/convert2rhel/main.py", line 115, in main
    pre_ponr_conversion()
  File "/usr/lib/python2.7/site-packages/convert2rhel/main.py", line 246, in pre_ponr_conversion
    subscription.disable_repos()
  File "/usr/lib/python2.7/site-packages/convert2rhel/subscription.py", line 853, in disable_repos
    loggerinst.critical("Repositories were not possible to disable through subscription-manager:\n%s" % output)
  File "/usr/lib/python2.7/site-packages/convert2rhel/logger.py", line 198, in _critical
    sys.exit(msg)
  SystemExit: Repositories were not possible to disable through subscription-manager:
  This system has no repositories available through subscriptions.
  
  
  Writing breadcrumbs to '/etc/migration-results'.
  Writing RHSM custom facts to '/etc/rhsm/facts/convert2rhel.facts'.
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