For large companies especially they are slow to adopt. To switch to blockchain it will be a huge expense. The tansition is not always seemless. People would have to be trained. The techmology is not yet prooven (though lots of companies are doing small scale tests). Most companies arent technology companies meaning that someone needs to develop packages for automobile, mining, oil, chemical, banking companies like ripple.

Thats the reason companies will want centralized blockchain companies. When something doesnt work they will want somone who they can call and chew on.