Don't know how much space/weight those bucket and spade charters would have for cargo when you consider full flights and possibly lots of baggage on 767/A330 types. Even with favourable winds, it is quite a lot of flying.
Don't Cargolux, Lufthansa and a few others run freighters from MEX to Europe.
Mexico is like Brazil in that there is a lot of produce and engineered cargo needing to get over to Europe and sometimes there is a backlog of available space.