They must think they have some secret sauce they don't want others to learn. How to optimally instruct sub agents for example. If they hide the sub agent prompts, other models cannot be trained to emulate.

Oh and you can't even use local models or other providers for the sub-agents. You're locked-in.

What’s stopping you from creating a plugin (MCP or Skill) that acts as a subagent? The plugin could use a local model.