Why does my terminal open with "Basic" settings
You probably just missed a setting. The "Default" button makes whatever you have selected in the Preferences menu the default.


(Selected in red)

I do find it kind of annoying that you can't set Terminal to just open with the default settings, so you have to change it in two places. edit - turns out I'm completely wrong, it does change the Startup automatically if you change the default. I guess I had the same problem as OP :P