I have written software that saves files and saves to standard geopackage formats.

Microsoft is known to have a lot of inconsistencies between its spec and reality. One important part of adoption open standards formats is that when you have real interoperability and competition between consumers of the format, the spec needs to actually work. HTML and the welcome demise of Internet Explorer specific markup through real competition in the browser space is a case in point

We can see from Fediverse that the spec still isn't really good enough. You have to code against Mastodon's code and Akkoma's code and GoToSocial's code. If you code against the ActivityPub/ActivityStreams spec, it won't actually work in the real world.

Same with most protocols. HTTP is followed closely enough, but forget about even strictly spec-compliant SMTP. Protocol specs are more like statements of intent.