Try think about a car which could be repaired and modified only by company X.
Now that would be a good business for company X. Company X could anytime
chose that now we don't support certain car models anymore, and if you happen
to have a car not supported anymore, then it is tough luck, but hey, you can
always buy a new car we support. We are very happy to sell you a new car!
Also, we can take your old unsupported car back to us and sell you a new car
a little bit cheaper, a rather good deal, (because we don't want that you buy
a car from our competitor).
Imagine your car being a black box none else can do anything but the company
who manufactured the car. Thus, a car would be like proprietary software.
Would it not be ridiculous and very bad for your freedom?
This is why educated people like free software.