I've covered this already in another post; Ubisoft is savvy enough to understand the importance of reaching a wider market than what their current platform supports. The question for them is which external platform is suitable to their needs. Overall they clearly expect Epic's to deliver, moneyhat or no. My semi-educated guess here is that Epic has shown that they have a very profitable userbase, meaning their users are more valuable in dollars than your average Steam user.
Also, I don't know what the DLC dealio is for uPlay games on Steam, but if Steam is taking a cut of all DLC sales too, then that gives Ubisoft an even stronger case for moving to Epic, as it'll increase the LTV for their titles significantly. If true, this would also detract from the idea that it's the moneyhat that'll make up for lost sales, because this won't cover the overall hit in LTV from DLC/MTX in the long term.