why? The same size PS file, one super-large and super-slow, the new build very fast？

There is a god given this, it really works.

What I want to ask again is, does adobe have no tools to clean it up automatically?

Edit menu >> Clean up, this is no use

Must rely on external scripts?

function deleteDocumentAncestorsMetadata() {
    //String version of the app name
    whatApp = String(app.name);
    // Check for photoshop specifically, or this will cause errors
    if(whatApp.search("Photoshop") > 0) {
        // Function Scrubs Document Ancestors from Files
        if(!documents.length) {
            alert("There are no open documents. Please open a file to run this script.")
            return;
        }
        if (ExternalObject.AdobeXMPScript == undefined) ExternalObject.AdobeXMPScript = new ExternalObject("lib:AdobeXMPScript");
        var xmp = new XMPMeta( activeDocument.xmpMetadata.rawData);
        // Begone foul Document Ancestors!
        xmp.deleteProperty(XMPConst.NS_PHOTOSHOP, "DocumentAncestors");
        app.activeDocument.xmpMetadata.rawData = xmp.serialize();
    }
}
// Now run the function to remove the document ancestors
deleteDocumentAncestorsMetadata();