https://www.pcgamer.com/ubisoft-explains-why-the-division-2-is-an-epic-games-store-exclusive/

Ubisoft surprised a lot of people in January when it announced that The Division 2 will be released on the Epic Games Store and not Steam—and that at least some of its future PC releases will be given the same treatment. Ubi said at the time that it believes Epic will "deliver a smooth journey," from preordering to release, and that Epic's effort to "disrupt" the industry is "something Ubisoft wants to support." 

Ubisoft CEO Yves Guillemot went deeper into the company's reasoning for changing stores today during an earnings call, and the short (and obvious) version is that Ubisoft believes it can make more money outside of Steam. So far it sounds like the strategy is working out well.