Because what you're offering is a service, and not someone else's software. Your added value is not actually in the code or the cute pictures; it's being available, having a low latency, allowing people with no tech knowledge to take part in the discussion, building a relation based on mutual trust rathet than serfdom. It's fundamentally the difference between a user and a consumer.

As an operator you're always making a tradeoff between the "negatives" of a license and the "positives" enabled by the actual software.

So for one example, the recent (bait and) switch of Elasticsearch to SSPL effectively means that for many actual real-world users of Elasticsearch, the benefits of staying on the official Elastic branch has ceased to be worth the costs of the license when your alternative is running FOSS Elasticsearch/Opensearch.

So to answer your actual question - presumably as an operator you want to use the AGPL-licensed code more than you want to avoid those same negatives of AGPL.

That's exactly why I license everything I open-source MIT/Apache.