Without any good quality backlinks pointing at your websites pages then as far as Google is concerned it's a case of 'no-one likes you and we DO care'.
Google's ranking algorithm is based on approximately 100 variables and criteria. 99% of which are known and utilised by SEO professionals. Some of these criteria are more important than others and it is widely known and proven that backlinks has a greater effect than most of the other factors. The relevance of backlinks when Google ranks your site is only equaled by having good quality content.
If you have no good quality relevant backlinks pointing at your site then you are in a popularity competition and none of the judges are voting for you - at all.
In this case how can Google ever work out from the millions of site out there which are the good ones and which are the bad?
The simple answer is they can't and since the very early days of Google the ranking algorithm has been -in part at least, based on counting the quality and relevance and volume of votes for your site from others sites. The do this ALL through backlinks.
As more and more companies and individuals have realised this fact then there is barely an industry on the Internet that can be conquered without having good quality backlinks and a good quality strategy to get backlinks for their websites.