Well it depends on why the company has never managed to turn a profit. A great example is Amazon. I think it existed for like 15 years before it first turned a profit because it was aggressively growing and spending all of their income to try to grow more.
As for Reddit, they are not growing like Amazon did. However, capturing a large user base is worth something because they may be able to monetize those users eventually. Investors view simply having a large user base as pretty valuable.