Stable context value with useMemo prevents cascading re-renders

What does this output?

let ctxRenders = 0;

function simulate(getContextValue, numRenders) {
  let prevValue = null;
  for (let i = 0; i < numRenders; i++) {
    const newValue = getContextValue();
    if (newValue !== prevValue) {
      ctxRenders++;
    }
    prevValue = newValue;
  }
}

let user = { name: 'Alice' };

// Unstable: new object every render
simulate(() => ({ user, login: () => {} }), 5);
console.log(ctxRenders); // 5 re-renders (new obj every time)

// Stable: memoized — same reference if user unchanged
ctxRenders = 0;
const stableValue = { user, login: () => {} }; // created once
simulate(() => stableValue, 5);
console.log(ctxRenders); // 1 (only first render)

Correct Output

5
1

Why this output?