That's not quite the order it happened, though:
1) Someone makes a platform, it's big and successful.
2) Private companies (banks, taxi services, streaming providers, education platforms) decide to only make apps for said platform, because the potential market of customers using anything else is too small to justify any business investment.
3) State says platform is so dominant apps are only on said platform and there's no choice - must be regulated.
4) State follows the same practices as private companies when making its own apps, for the same reasons as the private companies.