In short: because Martinet prioritizes running securely, running quickly, and letting you (the IT pro) control when Martinet runs.

Martinet should:

• run securely — if Martinet needs to be given permission to evaluate something, the permissions ought to be under the IT pro's exclusive control, not shared with a service.
• run quickly — Martinet should do its reviewing work, convey the report, and quit. Whatever system resources it needs to do these jobs should be returned to the system quickly. While a remote service won't use your hosting system's resources at all, Martinet's total runtime might be longer if many Martinet jobs are running simultaneously. Martinet might be delayed from running during an expected or desired time if many centrally-hosted Martinet jobs are queued to run.
• run when you want it to run — most services eventually go down for maintenance. It would be more convenient if Martinet could do its job whenever an IT pro required a report.