Lets be realistic: ESPN, or any sports network for that matter, is broadcasting events and sports that will draw viewers, so that sponsors and advertisers are willing to pay for coverage and timeslots (ie: how they make money).
With traditional sports, this is much easier for a number of reasons:
1. Familiarity. Kids (especially now), grow up playing traditional sports. They understand the rules of the games and can relate to them.
2. Accessibility: Name me one person that hasn't played basketball, baseball or football with friends at some point or another. You wanna try to be like Mike or LeBron? Just throw on some shoes and meet your buddies down at the playground....for free. Not many have true unlimited access to pinball machines.
3. Personality. People know the players in a lot of other sports. Even if they don't, there are a lot of interesting personalities that can be latched onto to sell interest. Did you ever see the King of Kong? That movie was awesome, but without the egomaniacal train-wreck portrayal of Billy Mitchell, it'd just be 2 dudes playing an arcade game. Not sure who this would be in the pinball world.
4. Vested interest. Team sports have a city or country they represent, and the outcome affects standings and has repercussions for other teams not playing as well.
5. Action! Lots going on and things can quickly change in who has the upper hand. No singular focus on one player for hours on end.
Cornhole has #1 and 2 cold.... And probably hoping for #3 considering some interesting people play it. Even that stupid American ninja warrior could claim a couple of these to keep it afloat. 2/3rds of that show is focused on individual personalities.
Pinball, while totally awesome, probably couldn't sell any of these points. Maybe if the top players were seriously crazy and things like &#!t-talking during play at that level was encouraged in-game, it could sell. But as is, likely never going to be the case.