[rjbwork]

I would guess it has something to do with tough lessons learned from their catastrophic early technical debt that brought the site and development to somewhat of a standstill right around 2009 or so.

See https://www.youtube.com/watch?v=eenrfm50mXw

[kristianc]

Many of the acknowledged leaders from a tech architecture standpoint started from the point of their architecture being a real mess. Soundcloud and Spotify come to mind.