The longer players explore a format, the more it becomes clear what card advantage engines are premier and format defining. As time goes on you start to see these cards over and over again in different combinations as weeks go on and metagames get solved.
At a certain point, if you’re exploring an archetype in a color combination that has a clear defined shell, it can be hard to find any reason to play different packages of cards. A good example of this concept in Modern can be found in the spell suite of Azorius Control. It’s hard to justify playing any card advantage engine besides Teferi, Hero of Dominaria, Jace, the Mind Sculptor or Memory Deluge. You might have ideas for alternative routes to take, but it’s unlikely at this point you’ll find anything better.
Another example of this can be found in Grixis decks. While many powerful options exist, it’s hard to beat the package of Lurrus of the Dream-Den, Expressive Iteration and Kroxa, Titan of Death’s Hunger as Grixis’s de facto grind engine. That being said, I’ve recently been working on a Grixis list that plays a new card advantage engine, one that not only feels robust and powerful but one that has been great against opposing Ragavan decks using the Expressive Iteration/Lurrus engine.