Well Blockbuster tried to force that format in the DVD market onto their customers. In most Blockbuster stores where the studio released both versions, Blockbuster refused to carry the widescreen for rental.
Hollywood Video on the other hand, embraced the widescreen format on DVD for rental.
I buy a lot of titles on preorder at 40% off MSRP. So for $20 you can own a title rather than $5.00 for renting it.
Which explains why you see dual sided DVD's. Widescreen on one side, full screen on the other.