Because that step is imo crucial, and it's unclear to me whether additional benefits of the roles are worth it over the basic review.
I can see how roles that ask the "planner" to explore other approaches automatically could be useful.
However, I don't have any interest in using small or dumb models for implementation when the subscription allowance permits using Opus 5.5 everywhere.
Work tokens are severely limited to the extent that if I used Sonnet 5.5 for implementation, I'd be out 2h into a session (Team 5x). +$400/mo. at API rates on OpenAI. So Haiku + Luna it is. There is no other way this is even usable for agentic dev at work. Works fine for people who multi-turn with a single agent.
Personal accounts I run the $17 Anthropic plan + $100 Codex Pro + DeepSeek. It's insane how much this stretches with this setup.
Maybe the crux here is how hands on you are with your sessions. As I've moved more hands off, I'm relying on other agents to take my place by embedding my heuristics into their config.
I've had an instruction to review the code with "claude -p" in place around the time GPT-5.5 released. I think it has served me well.
If I recall correctly it was before subagents were a thing. Even back then it was already automatic and would on its own request follow-up reviews or arbitrate a plan file if asked.