Vendor lock-in is risky and expensive for large corporations and governments, both of which tend to move slowly. I find it completely legitimate that a government would create a tool that's useful to its workforce and helps to avoid vendor lock-in. Insomuch as it's created by the government, it's released as open source.

Most companies and people aren't going to want to maintain the VMs and/or infrastructure to run their own platforms, so they have the option to continue using SaaS offerings like Notion.