The switch was meant to result in cheaper Macs but they’ve actually got more expensive.
The technology Apple uses is inherently more expensive. State of the art manufacturing node, wide RAM interface, custom memory packaging - these things are already expensive, and then you have R&D on top. It’s entirely possible that Apple can save a few $ compared to what they paid Intel and AMD earlier, but it won’t be a huge per unit difference. Of course, there are also other expenses, like display panels.