Aspect Ratios On Demand

I understand there is a popular opinion that movies should be viewed the way the filmmakers intended it to be viewed BUT we would often be doing so in an actual theatre if we did that. I elect we don't abide that sentiment or at least we don't ALL have to, as such, I would like ALL of my purchased movies shown On Demand in that format adjusted to completely fill out a 16:9 aspect ratio. I would also like to know, as is, why SOME of my purchased movies remain in Cinema Scope(black bars on top & bottom) but some have the adjusted ratio I speak of? I know some movies go to theatre with a 16:9 aspect ratio and aren't fixed but the movies I'm referencing were fixed.