My guess is the main issue is latency and accuracy; a single agent without all the routing/evaluation sub-agents around it that introduce cumulative errors, lead to infinite loops and slow it down would likely be much faster, accurate and could be cached at the token level on a GPU, reducing token preprocessing time further. Now different companies would run different "monorepo" agents and those would need something like MCP to talk to each other at the business boundary, but internally all this won't be necessary.

Also the current LLMs have still too many issues because they are autoregressive and heavily biased towards the first few generated tokens. They also still don't have full bidirectional awareness of certain relationships due to how they are masked during the training. Discrete diffusion looks interesting but I am not sure how does that one deal with tools as I've never seen a model from that class using any tools.