1. People think of companies like Uber primarily as providers of a regular service to customers (similarly to how Airbnb or Netflix is perceived), but it's interesting to see the engineering chops needed to maintain this operation. 2. Given the relative youth of the company, the stack employed is quite modern and often uses cutting edge technologies in production and with real impact on custormers. Everyday users of these technologies usually only get 'textbook' explanations, but blog posts like these allow them to actually find out how these can be used in production, what the caveats are, how they interplay with other parts of the stack etc. 3. Some people complain that when a startup gets bought or implodes, their technology virtually disappears instead of benefitting the wider developer community for learning purposes (I'm not here to argue what the best practice should be, just stating an observation of a common complaint). By continually describing their engineering practices (similarly to Airbnb in their engineering blog) and open sourcing their non-business technology (e.g. go-torch), their experience lives on beyond the life of the company.
Last but not least, it build a positive ethos about this company in the developer community.