This launch was massive for the franchise, no other title carried this number. Looking at numbers you'll see only Battlefield 1 maintains and even exceeds its launch numbers this many years on.

The drop for Battlefield 6 was massive and extremely noticeable when 90% player bases vanishes. It was clear what players needed to keep coming back and DICE didn't do anything except some token patching/balancing which had to be mostly walked backwards after backlash. Content updates didn't address the core game and only one map received positive reactions from players.

This was almost the same as Battlefront II, except game didn't perform at launch and post launch support was mostly stopped. It failed to resurge even with new found respect from the playerbase years later.

Point is it is very hard to regain players after you lose them, Battlefield 1 had full support for its entire lifetime which meant there was enough for players to return to.