For me, this is simple. It's no different to 'real' sports. Whether it's motor racing, football, snooker, whatever.
I need to care who wins.
I need to know who the drivers are, I need to be able to relate to them. I need to understand the rivalries, the histories. There need to be heroes and villains.
Take this season's Renault Clio Cup in the UK. I've never watched that series before. Why did I look forward to it more than anything else on the BTCC programme this season? Because there was a titanic battle for the championship between 2 drivers who were, to me, a hero and a villain, after various incidents through the season. I was invested because I saw the incidents, saw their reactions, heard their opinions on it in post-race interviews.
Another good example - years ago, the Seat Leon Cup where the prize was a BTCC drive. As well as showing the races live, there was a programme on during the week that interviewed the drivers and really exposed their personalities - for better and worse.
I remember really having '**** Head' Shedden down as the villain, something I never quite got over. Every race he competed in, I had him as the villain. As he was actually good, it made it compelling viewing.
If you want people to care, you have to give them something to care about.
That's what the ACC series lacked, in my opinion. I drifted away after a race or two because one or two drivers (who I recognised from this forum) apart, I neither knew nor cared about who they were or how they did.
Bring me the stories. Whether they're from the front of the grid or the back.
Make it human. Make it personal.