Because they clearly don't often last that long in practice.
Are you saying you wished they lasted longer? Ok yeah that'd be great... but I mean they don't at the moment you can see that for yourself, so expecting it is an unreasonable expectation.
You can expect that cars should last a hundred years if you want... but you're going to be disappointed.
Tesla does not need those screens to last 100 years; but it’s not unreasonable to expect at least 15 - 20 years.
1: https://www.cnbc.com/2020/07/28/25percent-of-cars-in-us-are-... 2: https://carsurance.net/blog/cars-sales-statistics/
Depreciation has little relevance to the majority of used-car buyers who need a vehicle, not an investment. They drive it until it can no longer be driven.
What is more relevant to the lifespan of a car is durability and availability of parts. For example Honda shared parts between the Civic, CR-V and Integra so they are relatively easy to obtain even going back to late 90s models.
"...about 80 percent of all Toyota vehicles sold over the past 20 years are still on the road today." [1]
Used cars are an entry point into an automaker's brand, and they do indeed want their cars to last as long as possible. Furthermore, reliability is a pretty large factor in resale value, and by extension, lease rates.
[1] https://pressroom.toyota.com/america-best-selling-car-camry-...
We're flying airplanes that are 30-40 years old. 18 wheel trucks are routinely driven a million miles. I think we need to adjust our expectations that cars need to be replaced every 5-10 years because they're no longer reliable. That's not a wise management of natural resources.