Great topic. Part of the issue is probably a transition from algorithmic approaches to data-driven approaches. What did previous users search for and click on?

Great topic. Part of the issue is probably a transition from algorithmic approaches to data-driven approaches. What did previous users search for and click on? Existing companies have a huge advantage from years of data, and not the kind of advantage that others can learn from (compare to publishing a better algorithm). Another factor may be that parts of the problem can separated out and are studied on their own, such as natural language processing.