Why? Nationalizing something is usually done only when it doesn't make sense to try and operate it based on a profit motive. Simply nationalizing things because there is only one or two of them is a weird criteria that isn't used by any European democracy that I know of.I don’t see anything wrong with forcing developers to make apps available for all platforms if it prevents one platform from being able to gatekeep certain apps.
Sounds like we need to nationalise these operating systems since competition has failed.
Forcing developers to make their apps for all platforms is bad in one primary way (and many secondary ways), it makes it much more difficult to enter the app development market. Right now a single person can build an app for either iOS or Android and have some small success at it. Requiring them to support two platforms would force them to hire additional staff or slow them down and make them less competitive vs larger teams.