This decision was made by @mabolek, since we want to get people to post their questions on https://talk.typo3.org primarily, so they are publicly searchable and indexable. This leads to less repeatedly asked questions, as happening in Slack (or other places that rely on real-time communications).
In line with https://github.com/TYPO3-Documentation/TYPO3CMS-Exceptions/pull/156, this also replaces the link to Slack in the footer of get.typo3.org with a link to TYPO3 Talk, reasoning being: