The model 3 and Y are basically the same car at a very similar price point. The Y is a 3 that spent too much time at an all you can eat buffet. It makes total sense to drop the refreshes at similar times because they share so many parts, including the parts being refreshed like the headlights and tail lights. It may not happen at the same time, but I’d wager within a quarter or two.
A 3 series and 5 series are completely different cars in different price brackets. Your typical 5 series buyer wouldn’t consider the 3 series because it’s simply not as premium in its finishes.
A much better analogy would be something like a Fiesta and Puma or a 208 and 2008. Given the fiesta is discontinued, it’s probably not the best analogy but the 208/2008 refresh happened basically at the same time.