Because where I'm from, traffic lights are not allowed to be set up like that. No simultaneous green for crossing traffic flows, unless otherwise indicated (eg, an extra warning light+sign under the turn's traffic light flashing when it's green and off otherwise).
What's not simultaneous is a green turn arrow with a green ped crossing. Intersections in the US are designed so that a green arrow will mean the driver has no conflicts and can proceed.
Not everyone (both drivers and peds) understands that distinction.
Direct link: https://i.ibb.co/Hn36L27/Green-crossing.png
solid green (right turn allowed) + pedestrian green (for crossing).
car and ped both have access to ped crossing. (Car should yield to any ped in crossing.)
Also, I drew a picture before I realized that this wasn't what you were asking about. But I like the picture.
C
A
R
2
|
v
--------- --------
CAR1 ->
---------|ped -> -------
| |
| |
| |
C
A
R
2
--------- --------
C
---------| pAed -------
| R |
| 1 |
| |I can't think of many places that I drive where this isn't the case.
The pedestrian crossing lights are in sync with the traffic lights, if traffic going N/S is green then the pedestrian lights going N/S will also be green even if cars are turning E/W
While vehicles are traveling north and south, the walk sign for crossing north and south is available. But vehicles are typically allowed to turn in the same cycle, protected lefts with their own cycle are common. Some intersections have a dedicated arrow for right turns and those will signal no rights while a walk sign is on, but otherwise pedestrians and right turns conflict.