There's a common misconception that many smaller earthquakes can prevent a larger earthquake. But every seismologist will tell you that smaller earthquakes do not prevent a larger one.
Smaller earthquakes release stress at small fault sections, thereby increasing the stress at the larger overall section, until that section has reached its full strain budget.
That's why after some decades/centuries (depending on a region's geological setting) a large earthquake happens, rupturing a larger part or the entire fault.