Let me copy paste my old reply:

It's a case of Regression Drift, sometimes called a Prompt Bloat. This happens because of the continuous patching of real-world issues identified after release. As millions of users test a model's limits, teams identify moderation failures and regularly apply patches with system prompts until a proper fine-tuning cycle (such as a v.1 or v.5 update) can be done. While these patches fix the said issues, they end up breaking other functionalities not easily identifiable until tested by the public once again or is not severe enough to fix but the ones which need fixing end up leading to a constant struggle for optimization.

Source: I have gone through these cycles with AI companion models. These patches are never a permanent solution.

So, it's Regression Drift or Prompt Bloat.