It's cavernous back there.
One of the biggest advantages of a hatchback, as compared to a traditional sedan with a trunk lid, is that the space within is usually larger and almost always far more accessible and versatile. of course, this holds true with the Model Y hatchback, as compared to the Model 3 sedan.
This video aims to prove a point in regards to the spaciousness of a hatch and it does so quite well. As you'll see in the clip, the Model Y is stuffed full with several larger suitcases, which we don't believe would fit so well in the Model 3. You can see that the height of the suitcases is such that they'd be very hard to shove into the Model 3's trunk opening. However, with a huge hatch fully open, stuff fits in with ease.
What do you think about the amount of gear that fits within the Y? Seems rather impressive, doesn't it?
Video description via Tre Loren on YouTube:
Tesla Model Y's Insane Cargo Space with 5 passengers!