A bolt-on lives next to the record, not inside it. Every action crosses a seam: read the context out, do the work, write the result back. Each crossing adds latency and drops detail, and the detail it drops is exactly the context that made the agent useful.
You pay for that twice — once in the subscription, once in the trust your team withdraws the third time the assistant says something generic. Native systems remove the seam because there is only ever one system of record.