You overestimate how much people want headphone jacks. Most people today use Bluetooth headphones and don’t miss their headphone jacks at all. I honestly forgot that my phone lacked a headphone jack until you pointed it out. That is how little I use wired headphones.
Moreover, why would every manufacturer copy a design that consumers don’t want? If the feature is so widely desired, it would only take one manufacturer not removing the headphone jack to win market share. Your model of the world requires every manufacturer to be incompetent in the same way. A much simpler explanation is that phones are a very competitive market and the manufacturers have calculated that, like physical keyboards, headphone jacks are not a feature most people care about. They prefer the headphone jack be sacrificed for better water resistance, better battery life, and lower cost.
Moreover, why would every manufacturer copy a design that consumers don’t want? If the feature is so widely desired, it would only take one manufacturer not removing the headphone jack to win market share. Your model of the world requires every manufacturer to be incompetent in the same way. A much simpler explanation is that phones are a very competitive market and the manufacturers have calculated that, like physical keyboards, headphone jacks are not a feature most people care about. They prefer the headphone jack be sacrificed for better water resistance, better battery life, and lower cost.