Google (and Amazon AFAIK) do give people resources to study with before an interview. Facebook sent me an electronic copy of CLRS beforehand.

I think the real question is: would making the interview process more accessible through offering courses increase the average quality of hires? Or allow more hires of the same quality? That's not clear. The actual white-boarding is pretty far divorced from day to day work, even at BigTechCo. An argument could be made that self-driven prepping for an arbitrary filter is the actual thing being tested, since it correlates more with success. Courses, although reducing the noise that comes from differing levels of prior exposure to those types of questions, would simultaneously decrease the self-motivation signal.