Because most companies are ruthless penny-pinchers and over-optimizers. They're willing to burn dollars to save pennies. The reason is that they're trading things they can measure for things they can't.

Basically, if you remove the knobs you can save, say, 10 dollars on every vehicle. In return, you have made your car less attractive and will lose a small number of sales. You will never, ever be able to quantify that loss in sales. So, on paper, you've saved money for "free".

Typically, opportunity cost is impossible or close to impossible to measure. What these companies think they are doing is minimizing cost. Often, they are just maximizing opportunity cost of various decisions. Everyone is trying to subtly cut quality over time.

Going from A quality to B quality is pretty safe, it's likely close to zero consumers will notice. But then you say "well we went from A to B and nobody noticed, so nobody will notice B to C!". So you do it again. Then over and over. And, eventually, you go from a brand known for quality to cheap bargain-bin garbage. And it happened so slowly that leadership is left scratching their heads. Sometimes the company then implodes spontaneously, other times it slowly rots and loses to competitors. It's so common it feels almost inevitable.

Really, most companies don't have to do much to stay successful. For a lot of markets, they just have to keep doing what they're doing. Ah, but the taste of cost-cutting is much too seductive. They do not understand what they are risking.