Likely due to areas that still have only 2g coverage. Still a lot of that in rural usa

What areas are those? From some quick research, the only carrier left that provides 2G coverage is T-Mobile but they're phasing that out this year.

Just because the map shows you can get 5G (or 4G) does not mean you'll actually be able to use that network. It's tricky and telecom companies like to play these bullshit games. It's pretty similar to how they'll advertise "up to X MBPS" internet speeds but the average speed is far lower.

You'll actually have these experiences in congested cities. Ever go to a concert and realize you don't actually have cell service? That's because the tower is fully occupied. Unfortunately phones might not report this to you and might not report the downgrade. Making Android and Apple complacent...