Taking too long for my parcel

I've been ordering from China for a while now, and recently I've noticed that the packages with tracking number are taking longer than ones without it. With this site I noticed that the tracking number packages take about two weeks to leave China. Does anyone know why this is happening? It's not because of the holidays because this has been happening since September, and it's still happening and it's only with the ones with tracking number, the other ones are not like that. Thanks!