My understanding is that the real estate needed is the biggest factor, not the grading, substrate, curbing, and paving.
They do take up a lot more space and as far as I can tell will create more accidents.
Photo of roundabout.
https://streets.mn/wp-content/uploads/2017/11/07Are-Roundabouts-Safer_535.jpg
Here is one by my old high school in Crystal, MN. I just noticed it earlier this year on a map so it must have been built not long ago. It looks like they have removed a house on the right. I bet many accidents have happened there.
https://www.google.com/maps/place/Douglas+Dr+N,+Crystal,+MN/@45.0035566,-93.3606001,406m/data=!3m1!1e3!4m5!3m4!1s0x52b3341a5d149891:0x69ce397bf717688a!8m2!3d45.0271346!4d-93.3600922?hl=en