Kevin Magnussen says he is not yet missing the "strange atmosphere" of Formula 1.
The Dane lost his Haas seat at the end of last year but he claims he did not fight too hard to find another seat in the midfield.
"It can be a pretty hostile environment," he told the WEC Talk podcast.
"In Formula 1 it is not really possible to compare between teams, so the way to advance is to beat your teammate and beat him by a lot.
"That becomes a difficult environment to be in. And it’s not really fun, because in Haas I was with Romain Grosjean and I really liked him a lot but we both knew we had to kill each other completely to move on.
"It just creates this strange tension and strange atmosphere," Magnussen added.
"It’s certainly the main reason why I didn’t really try to stay in F1."
Magnussen, 28, said once it was clear he would not get a seat with a top team, he decided to look elsewhere. Like his father before him, he has switched to American sports cars.
"I really like being able to work properly with my teammates rather than fight with them," he said.
"You can feel here that people are having fun and enjoying it much more," he told reporters at the Sebring circuit.
"People are smiling and everyone is much happier. Formula 1 is very competitive. So is IMSA, but in a different way."