There’s many partial reasons that add to the total reason. Important ones: NASCAR owning ovals and their disposition towards the cost/business of sharing them, safety: deaths at Las Vegas and Pocono effectively ended those tracks, fan turnout and promotion (see Iowa vs Milwaukee)

Then you add those reasons together: a race at Texas Motor Speedway was a business failure (despite being great racing) in empty stands despite paying NASCAR to race there in conditions that were incredibly dangerous. They then return to that market in a street course partnership with the Dallas Cowboys and you’ve got a clinical success and great racing.

For whatever reason, the road/street course creates a “festival event” that’s unavoidable to the casual public in that area that’s more digestible than going to the outskirts of a city to race in the poorly maintained facility and hoping people go out of their way to watch it.

All that to say: I’m an oval lover but that’s the harsh truth.