Conbini meals only register as "high quality" to you because your comparison point (e.g, American 7-11) is an abysmal excuse for food. The food is, in reality, not that special.

The first few years in Japan I loved combini food because of the novelty. Then you realise it's still processed crap loaded with chemicals and usually nutritionally poor (lots of rice, very little veg or protein) barely better than supermarket "ready meals" (or bento/souzai) and more expensive.

It's the honeymoon effect I guess.