I definitely can understand how these teas are so popular. I've tried both of the examples you give too, and I think they're both pleasant and drinkable.
Why are they so popular? I think both orange and cinnamon are familiar and well-liked flavors for the typical American palate.
The other traditional spices in masala chai are, I think, less familiar. I think cardamom is especially less familiar to the American palate, and perhaps ginger...and then pepper is familiar but not usually associated with tea or anything sweet. Look at Indian cuisine--it's totally dominated by cardamom, and it uses pepper in sweets, so it makes sense that these would be popular in their spiced tea blends.
I personally don't like the blandness of mainstream American tastes...I think what makes food in the U.S. great is all the diversity and ethnic food, and the "default" food I find far too bland for me. But I think that the relative presence of orange and cinnamon in mainstream foods in America probably explains the popularity of these blends over the more complex and traditional masala chai blends that include spices less commonly used in the U.S.
Me though? I'll stick with the traditional masala chai, and I personally omit cinnamon and go very heavy on the cardamom.