I think it is because the changes are, currently, considered esoteric and slightly experimental in the sense they want to reserve the right to make breaking changes to them. SQLite has a relatively slow cadence when it comes to things like this. Other reasons may be that they're still working on the tests to validate and support those features - as well as documentation. I am hopeful BEGIN CONCURRENT and WAL2 will make it into the amalgamation at some future date.