When a manufacturer sells a car, that's it, their entire income. Many of the forecourts where you actually buy them have a garage attached, willing to offer you servicing in order to continue making money from you, but little of that (if any) makes it back to the actual car company.
The average car has a lifespan of ten years. Most people don't keep them for the entire ten years, they'll likely have a few owners through that period. Still, it's a long time not to be making any money from a product.
During the recent recession, new cars sales dried up and threatened to put many car manufacturers out of business (it did to some), while car owners preferred to hang on to their existing models a bit longer. Where work on repairs may have been enough for someone to consider a new vehicle, it was being done instead.
I happened to be reading an article about new car technology (as CES is on) and thought how it would be many years before it made it to me, even if it goes into this year's models. Which made me wonder why car manufacturers don't offer upgrades.
I'm not saying it would be easy, but if they started at the design stage they could build the capability in. The option to swap out components on the dashboard to give you new technology, for example. I use an aftermarket Bluetooth unit for hands-free in my car, but it would be better to have it built-in (at a reasonable cost).
There is a thriving aftermarket in some technology products (e.g. in-car entertainment), but not for steering or braking systems, gearboxes or engines. Newer models have advantages in better fuel consumption, improved power, all the lessons learned in the intervening years.
A typical model appears to last five/six years before being replaced (it used to be much longer). So even within the timeframe of a single model there is scope to issue updates.
That's before you get to options that people may not have been able to afford at the time they bought the car, but would like to add as they go.
Changing cars is a risk, especially if you're buying second-hand. You may get a pearl that will give you no trouble, you may buy one plagued by gremlins. So when you get a vehicle you like, wouldn't you rather upgrade it than spend time and risk on a new one?
The car manufacturers can then make ongoing money from their various models rather than being forced to focus on how to sell people a new vehicle. They can build relationships and loyalty. Plus it provides an extra revenue stream.
Cars are complex machines these days, so it's not something I think would be easy, but maybe the shift to electric, which have much more contained power units (engines) that can be designed to be easily detached from the other systems will allow this.
The question is, will anyone except a few giant companies be buying cars when they all can drive themselves? Why would you want the associated hassle and cost of owning something that will be parked for most of its life?