It is safe to say that Ultimate Team is by far one of EA's biggest money-making machines. However, you may not even realize how much of the company's profits are generated by this mode. According to the company's report for the previous fiscal year (ended March 31), as much as 28% of the total income came from the UT. This amount includes income not only from FIFA but also from other EA sports productions where Ultimate Team (Madden NFL, NHL) is present.
Electronic Arts informed only that a "significant part" of it comes from FIFA, but we didn't learn what the exact amount was. As we all know, Ultimate Team has recently become one of the cornerstones of the company's business model.
This "surprise mechanics" is controversial all over the world. The chances of EA giving up this type of lootboxes are small and it's hardly surprising, since the profits from selling packs in the game are higher than the profits from selling the game itself (FIFA sales are responsible for only 14% of the total income in the previous financial year).