Just curious about Solid's update algorithm

[AFatNiBBa]

I got an error that is ONE HUNDRED PERCENT my fault, but it happens because of this part of Solid's update algorithm.
The following (nasty) code approximately reproduces my error (Also available in this playground)

import {
  type Accessor,
  batch,
  createMemo,
  createRoot,
  createSignal,
} from "solid-js";

function preventCircular<T>(f: Accessor<T>): Accessor<T> {
  var running = false;
  return () => {
    if (running) throw new Error("A memo called itself");
    running = true;
    try {
      return f();
    } finally {
      running = false;
    }
  };
}

createRoot((_) => {
  const [a, s] = createSignal(0);
  const b = createMemo(a);
  var c: Accessor<number> | undefined;

  const d = createMemo(() => {
    // This memo needs to be nested for the error to come up
    c ??= createRoot((_) => preventCircular(createMemo(b)));
    return c() + 1;
  });

  // The batch is needed because we need to update the inner memo ("c") first, which will then cause the update of its parent ("d"), but only if the update goes through the change of a memo ("b"), the change of a signal ("a") is not enough
  batch(() => {
    s(4);
    c!();
  });
});

To fix my error, I think it would be very helpful to understand why it's needed to update the ancestors, does anyone here knows the reason?