Well, they're more ergonomic because you can align your hands with your arms, instead of twisting your hands at an angle. This is a matter of fact. You are entitled to prefer a flat keyboard -- that's entirely your choice -- but it doesn't change the ergonomic reality.

> Besides, people also use laptops and may not want to swap their keyboard.

Laptops are not ergonomic, and nobody who knows the facts will use them for long periods for precisely that reason. However, you can make them less damaging to your health by putting the laptop on a riser and using an external keyboard.