First, you're using the terminolgy slightly in error. All theatrical movies made after the mid 50's are in widescreen. What you mean is why are there so many Blu-rays made in the "Scope' type of widescreen which is movies with wdths of 2.00 or wider.
Why are many Blu-rays from movies in that shape or widescreen format? because seems many directors prefer to make action and sci fi and epic movies with that format and many people like those movies so that's why.
You like James Bond movies? Most were made for "Scope" Star Wars all were made for "Scope", Spider-Man? 66% were made for "Scope". Pirates? Scope. Matrix? Scope, Lord Of The Rings? Scope.
Now why is you TV not "Scope"? Because there are many TV programs and movies not made in "Scope" Some are in 1.33 (analog TV and Silent films) and 1.37 (Sound movies before the mid-fifties). Some are in shapes of between 1.66 and 1.85, (European widescreen movies many Disney widescreen movies, US movies, from the mi-fifties on, that weren't made in "Scope" or 70mm etc formats), plus the new 21rst century TV programs for 16:9 TVs (which are 1.78 wide). And 1.78 was chosen because 1.78 falls geometrically in between 1.33 and 2.39 movies and because when it was chosen as a shape, TV manufacturers knew TVs with that shape would be plausible to manufacture.
Most Scope movies fill 75% (3/4ths) of your 16:9 screen's real state, not 2/3rds (66%) btw. That is, if the TV doesn't overscan. If it does, the figure is closer to 80% (4/5ths)
For more info see:
Black bars? 4:3-16:9-2.35 Widescreen Fullscreen Scope OAR sticky threads
There are many BDs (and movies) that will fill your screen (there's a few threads where they list them or give links to lists of them) and there will be more.
Mmm I see while I wrote this reply several replied!
