For me, it is just so easier to push down on the brake lever with most of your hands still on the bar. I have to move my hands much more, and sometimes move my fingers off the brake lever, put them on the bar, to push on the trigger in order to shifter. If I'm still holding onto the bar, I feel like I would pull in the brake lever when shifting.

I guess it's whatever you're used to, and many people don't give STIs a proper chance when it is indeed a great product. Again, most products aren't designed for everyone, and this clearly is one of them.