Reasons I can think of (unrelated to YC/HN though):
Fostering a community of tech-savy people interested in the latest technologies increases their brand size. HN is also a place where YC-related companies can advertise to and hire like-minded people. This in turn would increase the chances for those companies to succeed.
Regarding costs: I believe this site is hosted on one somewhat beefy machine, maybe two for redundancy. Compared to reddit, this site is (I believe) comparable to one active subreddit (Reddit has 100s of those), without image or video support. It has a rather simple domain model, only marginal styling, and has generally only a low overhead per page loaded, making it a rather lightweight application for the amount of traffic it receives.
Also, if you're interested, (parts of) the sources of HN are available here[0], it's a rather lightweight server in a dialect of Lisp.
Fostering a community of tech-savy people interested in the latest technologies increases their brand size. HN is also a place where YC-related companies can advertise to and hire like-minded people. This in turn would increase the chances for those companies to succeed.
Regarding costs: I believe this site is hosted on one somewhat beefy machine, maybe two for redundancy. Compared to reddit, this site is (I believe) comparable to one active subreddit (Reddit has 100s of those), without image or video support. It has a rather simple domain model, only marginal styling, and has generally only a low overhead per page loaded, making it a rather lightweight application for the amount of traffic it receives.
Also, if you're interested, (parts of) the sources of HN are available here[0], it's a rather lightweight server in a dialect of Lisp.
[0] https://github.com/arclanguage/anarki/tree/master/apps/news