I actually just happened to be doing analysis on movie box office data, and found exactly the pattern of which you are describing to be something worth while for further investigating. I am a data scientist student at this bootcamp called Metis and we were tasked to do analysis on data from boxofficemojo.com. I found that actors that have done well with other actors in the past, tend to help make successful movies. This pattern also seems to exist with past director to actor relationships. Now while I believe this is slightly skewed by movie sequels with similar casts it seems to be pretty consistent. If you like I can post my analysis blog post about it once I’m done editing it? Good eye lol.