Why is everyone so mad about this feature? Maybe I do not understand Server Push in http2, but isn't it useful to e.g. send a rendered picture to the client ins

Why is everyone so mad about this feature? Maybe I do not understand Server Push in http2, but isn't it useful to e.g. send a rendered picture to the client instead of the client polling the server every 5 ms until the image is ready? What about chat applications?