Why Aren't We Able to Set arrival_time in Driving Mode?

[çağlar çınar]

I'm trying to create a simple app that notifies the users when they need to leave the house to arrive somewhere at a specific time. And Developer's Guide clearly says it's for transit mode.

For that, I'm trying to use the arrival_time parameter in the API but apparently it doesn't work when the mode is set to Driving.

I know it kinda depends on the departure time but still it doesn't make too much sense. Because think about it, I can get that data by guessing a departure time, getting the time_in_traffic parameter, add it to my departure time and compare it with my requested arrival time. If it's not the same, keep calling the API with later or earlier departure times until you get the right departure time.

Why isn't the option to set the arrival_time in driving mode given to us? Is there a reason? Am I failing to see an obvious reason or something?

Google Maps is already giving us the suggested departure time when the arrival time is set, and I don't understand why API doesn't also support it.

Or at least can anyone suggest me a solution to do this other than that tedious multiple API calls solution.