They also spent those 2000 staff implementing image hosting, video hosting (poorly), a live chat feature nobody wanted, maintaining a mobile app that was inferior to several apps being developed by lone independent coders, and a bunch of other nonsense unrelated to the core experience of Reddit. Rather than being the best Reddit the could be they tried to poorly mimic Facebook and Instagram and other such social media sites.
The thing that killed Reddit was the unfortunately extremely common drive that corporations feel to grow, grow, grow grow all the time every quarter. Always must have more subscribers, more features, more income streams, more products, new markets.