I'm not sure. Anthropic probably feels safe enough for the foreseeable future given that they've been focused heavily on business customers (cowork, claude code) who just pay straight up for the service.

Whereas OpenAI seems to be huge in the consumer market (where downward pressure on pricing make ads more likely). They're trying with Codex but all the other stuff (the legal, financial, tooling with cowork, etc) seem to be a lot more fleshed out on the Claude side.

So they can probably get away with this for a while. That's my guess though.