It's not "how hard is it to fix?", it is more like "how hard is it to keep up with competition?", where competition in this case are Travelocity and the likes.

The answer is that Travelocity, Hotels.com, Expedia will always be better, because reservations is their business, when for Starwood, Hilton, etc. it is just one aspect of their business. And that's why there is only one sure way for them to entice people to use their inferior booking engines - bonus points.