Maybe after his awful decision MK9, Raiden decides to take a step back and let the mortals control their own destiny. And has more of a guardian/mentor role than a hands-on role.
This may or may not allow Fujin to enter the forefront. I kinda hope it would but I don't want two returning gods. I much prefer Fujin to Raiden but we don't need another payable or mainline story God IMO.