Why do we have renin in the renin-angiotensin-aldosterone system? Why don't we just skip the first step (angiotensin I) and get directly to the active (angiotensin II) peptide?

What advantage is there to having renin? It seems like simply a middle-man that is unnecessary. Why even bother evolving renin in the kidneys when a person could simply have a modified angiotensin-converting enzyme that produces an active angiotensin II directly from angiotensinogen?