Apps need to be written specifically for the VM platform, and have a commercial agreement with Virgin - they're then installed for you.
It's not like Android or iOS where you go to an app store and install whatever you like.
Disney+ I'm sure is on VM's radar, but there's been a couple of reports of Sky having an initial exclusivity period, and some others where VM bosses have commented to the effect of "I'm sure we'll have it early 2021" or similar.
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