First, a crucial clarification. "All The Fallen" is not an official Expansion Pack (like Get Together or Seasons ). It is a third-party created by an independent modder known as ColonolNutty (and later, other creators who forked the code).
The short answer is:
Narrative and Agency
: Following reports from players and the mainstream community, platforms like Sims Fileshare have actively removed these files from their servers. Investigation All The Fallen Sims 4