Alot of directors, especially big names with iconic styles tend to have people they often work with. Coppola worked a bunch with John Cazale (RIP), Robert Duvall, etc, Kurasawa's partnership with Mifune is iconic, Billy Wilder worked a bunch with Hitchcock with Jimmy Stewart, Nolan worked a bunch with Michael Cain, Tarantino/Samuel L and Uma, and Cillian Murphy, etc.Scorsese clearly enjoys making movies with the same actors. He's made close to a dozen with De Niro and a half dozen with DiCaprio and has two more upcoming that star DiCaprio. What probably appealed to him about this one is that he could make it revolve around both. I doubt that he would've been interested if the focus were elsewhere. He seemingly enjoys the process of making movies with friends and isn't too concerned with pleasing anyone else (hence, long run times, for example). That's probably always been the case, but feels like even more the case in recent years... not that I blame him. He's 80, and if he wants to make 3.5-hour movies with his friends, he's earned the right, but I'm not as keen on watching them.
Scorsese has the people he's often used such as DiNiro, Pesci, Frank Vincent, Harvey Keitel, etc. But, I'm sure if you looked at a lot of directors people would call auteurs you would find similar overlap on who they cast.
Outside of maybe Kurosawa/Mifune, I would say Scorsese/De Niro is probably my favorite director/actor combo of all time, only others in the discussion are Leone/Eastwood (although weirdly my two favorite Leone films don't have Eastwood), Tarantino/Samuel L, and Hitchcock/Stewart.