Canisters for storing roll film are available separately at some of the larger mail order firms.
I think the reason for not using canisters with roll film is mostly historical. The backing paper system was developed very early, and it has worked very well. Since it worked well, and there was a lot of existing equipment, why change? Until a few years ago, everyone knew how to handle roll film. It was slow, but so what. There is always the possibility of dropping a roll and losing all the exposures, but that seldom happens. When the Instamatic was developed (and later the 110 and disk cameras), Kodak decided that quick and easy film handling would be a selling point - and it was. Roll film for these (OK - it was 35 and 17mm stuff, but it was treated like roll film) became packaged in an easy to handle canister. The history of 35mm (and 70mm) was different. These films were originally movie films, and the equipment was designed to use the sprocket holes. The metal cassette was an easy way to make small lengths of film available. Up until about 45 years ago, all the 35mm cassettes were reloadable. The system worked, and it became a standard.