Based on their presentation they are building the cars to last that long. All the electronics and everything else is designed to last. If you look at the video

Based on their presentation they are building the cars to last that long. All the electronics and everything else is designed to last. If you look at the videos of the Model Y breakdown you can see that they did a lot of stuff that is slightly more expansive but should improve lifetime. They want to be able run these vehicles into the ground making profit for them, specially after coming of leases.