Lmao why do NPCs always foist their funeral ceremony on our Sims?

Well once you start a save everyone's lifespan is at the beginning of the life stage and everyone ages at the same rate. That means a bunch of Sims will be aging at the same time eventually reaching the elder stage at the same time and all dying around the same period (since elders don't all live the same amount of days).
This is why sometimes you might have a ton of sims dying at once.