One day/week fantasy leagues--how are they not gambling?

I listen to a bunch of podcasts, and on a bunch of the podcasts I listen to, I’m treated to a lot of ads for sites like Draft Kings dot com and Fan Duel dot com. Basically, these are fantasy sports websites, offering cash payouts and requiring cash buy-ins. What makes them different from fantasy leagues generally is that, depending on the sport, they’re one-day (baseball) or one-week (American football) leagues.

I’m curious how in the world these guys don’t get into trouble over the laws on internet gambling. I can understand and respect that a normal, season-long fantasy league has enough of a skill component to steer clear of these laws, but when we’re basically talking about Any Given Sunday, it seems like the random chance would overwhelm any skill involved.

Am I missing something here? Why aren’t the Feds shutting these guys down?