The bells were prone to theft, so the state decided to step in as caretakers, replacing bells whenever they went missing. Imagine a state legislature today saying, "Sure, why not. We'll allocate funds every year for something nonessential." There must have been some heavy-duty lobbying to make that happen. At least the replacements were made of concrete to save money and make them less attractive to thieves.
Furthermore, claiming US101 follows the historic El Camino Real is playing fast and loose with the facts. As this article explains:
The message implied by the presence of the mission bells -- that motorists' tires trace the same path as the missionaries' sandals -- is largely a myth imagined by regional boosters and early automotive tourists.
What? Businesses making things up to attract customers? Unheard of!