[burntoutfire]

For the same reason why Hollywood producers pay $10m for a Brad Pitt, where they could get some rando who looks and acts just as good for $100k - Brad is marketing device, the movie will get much more publicity because of him, and people will go see the movie just because of him. Same for Keanu here.

[overgard]

I'm curious if that's actually true though. A lot of recent huge hits in TV at least were made up of casts of either relative unknowns or people that didn't have huge star power anymore. "Stranger Things", as one example. Mad Men and Breaking Bad created a lot of stars, but they weren't famous to start with. The Walking Dead was the most popular show on TV for a long time and I can't really recall an A-lister.

Even a lot of much older shows didn't need star power. Think about something like Star Trek TNG. The most famous person on that cast when it started was Will Wheaton. Obviously Patrick Stewart became huge but he was a total unknown prior.