Ads are priced based on how many people are predicted to see it.
To get an ad on TV, you need to buy time on a broadcaster's network. Every second of outgoing signal is carefully budgeted based on projected viewership. Ads cost more when we know people are watching. Superbowl ads reach *millions* of people +/- tens of thousands. These ads cost ridiculous sums of money.
That budgeting of seconds of broadcast time doesn't exist on youtube. The cost to youtube to give you 10 seconds of advertising is basically zero. The cost to a broadcaster to play a 10 second advertisement is... a profit margin less than the cost of a 10 second ad on TV.