Because the legal system is not some mechanistic program that computes decisions over cases. The legal system is (for better or worse) based on human judges that look at the entire context and make judgments of what is reasonable or not. Given that this is an antitrust case, the business model is absolutely part of the context.
Selling something at below cost to gain market share is a classic anti-competitive tactic. This aspect of Sony's business model vs. Apple's seems like it would be very unflattering for Sony if they had more market share. It's lucky that Sony still has strong competition in the form of Microsoft and Nintendo[1].
My personal take is that by saying "Sony is different though" Epic is trying to provide a fig leaf for a platform owner that could cause them real financial harm if they got on their bad side.
Edit:
[1] Isn't it interesting thought that the 3 console platforms don't compete on what percent cut they take from software published on their platforms. All 3 are 30%.
