Honestly, betting probably isn’t the main reason games get fixed.

If not a single legal or illicit bet was made on a game, there’s still a huge reason for games to be fixed:

League profit sharing.

A lot of teams make their money from the league share. So it’s in every owners best interest for the season and especially playoffs/championships for there to be a good story every season.

More important than any single team winning, they want people watching on TV for that ad revenue sharing.