Mostly because of cost and aesthetics. It’s actually still a great dental repair material in terms of durability. I have a gold capped molar that I elected and pushed my dentist for after doing research, had a good conversation about trade-offs in materials vs going blindly with a default. My mother in law also has most of her fillings done with gold. But obviously it’s expensive and you need a dentist that is used to working with gold which is less common. Most people do not want front facing teeth in gold.