Why does Google show multiple results from the same domain?

This video talks about the reasons why there are multiple results from the same domain at Google searches. Matt Cutts chronologically discussed the efforts of Google engineers to solve this problem and any imminent problems to improve diversity in the search results and also to optimize user experience.

The video highlight the following points:

1. This question is the most frequently asked from Google users and the former had developed their search results throughout time to improve the diversity of search results in the first page.
2. After the commencement of the Google search program, they had set no restriction on multiple search results from the same domain and let the ranking depend on the keywords that can be found on sites. However, to resolve this bad user experience, they developed a program called host clustering which limits the results for each subdomain to two.
3. Overtime, people, spammers, and webmasters adapted and formulated a way of bypassing host clustering which allowed them to crowd the search results once again.
4. Google, once again developed their search results by limiting only one result from the same domain and intentionally made it harder for the results from the same domain rank.
5. Meanwhile, Google search prioritizes really good and legitimate websites about a certain topic by allowing those to rank multiple times in the search results. It gathered a lot of negative responses from users because only large websites almost monopolized the search results and people are disappointed as they misunderstood it as non-promotion of diversity by Google.
6. Google allowed flooding of search results from the same domain in the third and subsequent pages because only few people are browsing those pages therefore it is not much of a crisis for anyone.
7. Lately, Google had been developing a new system of improving diversity in the search results whereas second, third, fouth, etc. pages will not be dominated by a single domain but still allows the domination of authorities in a certain topic.
8. The development of Google search results is continuously evolving.

Points to take note:

1. If your domain talks about a specific topic, make sure that Google will treat you as an authority on that certain field so that it will rank your subdomains without being subject to their established limitations.