Where did you see that they are no longer making new content for Sims 4? The article doesn’t seem to say so and the last I heard they planned to release content for Sims 4 alongside Sims 5. FYI, I would prefer they stop with Sims 4 content.
Oh okay. A while back, their VP Lyndsay Pearson explicitly said they plan for Sims 4 to continue to exist side by side with Project Rene (aka Sims 5). I was wondering if that had changed. My cynical take on the plan to keep both going is that Sims 5 is probably going to be a live service abomination, which they wanted Sims 4 to be, so keeping Sims 4 might be hedge in case Sims 5 fails hard. Of course, they could also have been lying.