An office posed the question "Why do we have to click on Action / Create Appointment on touchscreen devices and only have to double click on an empty time slot in the Calendar to open a New Appointment window on the desktops?"

The answer is that if the touchscreen device is able to register an double click, then it will open the new appointment window.  If the device cannot register a double click then the office has to use Action and then click on the Create Appointment to open a new appointment window in the Calendar.

So this is working as designed according to the ability of the touchscreen device to register a double click.