The pro upsell option would be TB3/TB4/USB4 which itself is old tech now - like on the iPad Pro.
If a large portion of the market will never use those features, why not exclude them and make the phone $200 cheaper? and thus, we arrive at the reason why "base" and "pro" model product tiering exists (not just for apple either).
would it be nice if you got the 7800X3D for 7600 prices? sure, free stuff would always be nice.
is there an argument that if you're spending $1000 you shouldn't be compromising on features? yes, that's why I buy NVIDIA products and not just "we have a bit more VRAM" or "we're 5% faster in raster perf/$".
The real and only reason for not having USB3 in the iPhone 15 and 15 plus is because them using last-gen SoCs in non-Pro phones in recent times. Not because of cost, or power, or performance - it just only had a USB2.0 port so they put in a USB2.0 controller.
Completely coincidentally they also support 10Gb USB.