Pickup date and time not respected

Hi,

Is there a reason why we sellers (Easyship) are required to choose a pickup date and time interval if it won't be respected?

The pickup drivers come whenever they like, and sometimes they don't even show up on the scheduled pickup date. Most sellers are registered legal companies with fixed working hours, and the pickup schedule is set based on those hours.

So why do Amazon's third-party drivers come at random times and call sellers whenever they feel like it?