bitcoin.org is a privately operated website, independent from the Bitcoin Core project. Historically, new Bitcoin Core releases have been published on bitcoin.org as well as on the project’s own website bitcoincore.org.
You’ll need to ask the bitcoin.org maintainers why they haven’t put Bitcoin Core 22.0 on there. There appears to be an open request (https://github.com/bitcoin-dot-org/Bitcoin.org/pull/3765), but it has not been merged yet.
Update 2021-nov-16: this seems to be fixed.