If over time the time cost of intermediaries (additional handling and overhead costs) remains below the cost of the steps to eliminate intermediaries (the investment required to establish a 501(c)(3)) then I stand corrected.
As the person who runs the central CEA Ops division, I can promise you that it saves time and money costs, and doesn't impose any significant such costs that I can think of. Registering as a UK charity and a 501(c)3 (and a company that can have employees, interns and an office) has taken a lot of work, and I'm glad that GWWC, 80k, Effective Animal Actisism and The Life You Can Save haven't had to duplicate (or quadruple) that work.
PS: Despite this view, I promise it wasn't me who downvoted you :)
Both GiveWell and the Centre for Effective Altruism (CEA) --an Oxford-based umbrella organization consisting of Giving What We Can, 80,000 Hours, The Life You Can Save, and Effective Animal Activism-- have been discussed here before. So I thought some folks might want to know that these organizations are recruiting for a number of positions. Here are relevant excerpts from the official job announcements:
(Full disclosure: I'm friends with the co-founders of CEA and have donated to Effective Animal Activism.)