[edit: for clarity, I am not against roundabouts]
I don't have real expertise in civil engineering
Traffic lights have a smaller physical footprint and require less construction activity.
Traffic lights fit on a cost spectrum from two stop sighs, to four stop signs, to stop signs plus blinking lights, to non-trivial signaling.
First make it work. Then make it good. Then make it fast.
Engineering is not a one size fits all discipline.
[edit: I have a background in urban planning, architecture, and real-estate development]
The footprint is a cost problem once. They don't need power, computers, or technicians to come out and maintain the equipment constantly.
>The footprint is a cost problem once.
Land can approximately be converted to a recurring cost via rents.
You forgot roundabouts with traffic lights.
Here’s one in Australia near Perth:
https://youtu.be/h8lhX9Q6Z5g?si=eloUWLcH8q3eJiZH
And I’m certain I’ve driven through other roundabouts with traffic lights in other states.
My honest take roundabouts with traffic lights are just traffic lights with extra steps.
In England we even have roundabouts of roundabouts https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)
I’ve driven around the Hemel Hempstead one a few times. Very confusing when I first saw the sign.
Ooo! I like that one!
I know of a couple in NSW: one in Albion Park, and another in Bomaderry.
They work well when the peak-hour traffic tends to block some of the entrances. You can use the lights to allow the blocked entrances to flow, then turn the lights off out of peak-hour.
A roundabout can be as simple as a circle painted in the middle of an intersection, plus a bit of signage. It doesn’t have to be a big thing.