One could argue that, in the second case, you're IN the edit microflow settings pop-up when the modeler selects defaults. That means you can SEE what the modeler has done and have the option of changing values before confirming the defaults.
When dragging a microflow from the project explorer, the modeler would be implementing and saving a configuration without your consent, which could hide potential bugs from the developer.
Of course, that argument is mostly academic and not an actual problem under most circumstances. If it's really bothering you (which I can imagine) you should definitely submit a ticket.