My kids cross a road getting off the bus. A straightaway- always in daylight, without the sun shining in drivers’ faces- and in a 35 mph zone (so, not the same circumstances).
The bus driver does tend to wait to give the crossing signal if an oncoming car is approaching. But after he gives the signal, sometimes an oncoming car comes into the picture. The kids are usually good about checking that direction themselves, but they have their “off days” like any other young child.
It’s quite possible (and to me, not unreasonable) that the bus driver can give the crossing signal while an oncoming car is well out of range of the bus. If that car happens to be going faster than expected (35 mph), that could become a problem in a hurry.