Consider cost vs rewards, including diminishing returns on investment, customer requirements, and implementation.
There is no doubt that comparing position accuracy and tracking favors dual band GPS receivers. There are more points of reference and overall better tech thus better results. However that's only if you compare and track using satellites which isn't the way the iPhone works.
The iPhone (and I'm sure other smartphones) are using satellite position plus supporting location detection sources bluetooth, magnetometer, wifi, cell tower, accelerometer, and gyros (API and app dependent). Basically the iPhone is good at knowing its position in the world, much like you could be blindfolded and walked out of your house and around the block and maintain a firm understanding of where you are.
The iPhone GPS alone can get your position down to 1-5 meters outside depending on buildings. Even now I see ~6 meters and I'm inside about 3 meters from a sliding glass door to a covered deck.
Add accelerometer data and your tracking will remain spot on. Combine that with an app that error corrects by pulling your marker to the road/walkway and its pin point accurate (in reference to your map).
Customer requirements are a bit superficial in reality. The vast majority are using navigation apps on roads/walkways, like I mentioned these apps will error correct by pulling your marker to the road you are on/near. In reality if the map has a road 100 feet off its actual location, you are none the wiser because you are just going from point A to point B. It says you are are on a road, you are on a road, what does it matter if your position is precise? In many many many cases your GPS is much more accurate than the roads on the map you are using.
Cost vs reward is probably the most important thing. Apple minimizes GPS use outside of navigation apps for position tracking due to battery usage. Wifi can be more accurate, faster and more efficient if all an app needs to know is what town you are in, for that matter cell data can tell your app that. Now according to this study (
https://arxiv.org/pdf/1910.13041.pdf) the specific phones tested showed dual band GPS using 28-37% more power. That quite significant when it comes to real world usage.
Dual band mobile solutions currently leave a bit to be desired as well. A smartphone is like a Swiss army knife, it does a lot of things well but nothing great, its a convenience. To that end you'll see improvements in positioning but not the full benefits of L1+L5 bands provided by dedicated units used by emergency responders, air planes, surveyors, etc.
I think we will see dual band in the not so distant future but only after an improvement in the tech as far as accuracy and power consumption goes.
This is very typical of Apple. Wait to a tech to mature so it doesn't come with too many negative side effects. In this case it would be worse battery life and potentially higher cost (more cost to us or lower profit to them) to obtain a occasional increase in location precision in specific situations.
Just my thoughts. I know there will be people that need better location data however we really should keep the intended market in mind.
