It's an all of the above situation. Both Singletary and Moss were playing in an offense where everything was geared towards the passing game, and the O line was usually somewhere between terrible and mediocre. I have no idea how good the O lines in Indy or Texas are, but since Indy has been leaning on Jonathan Taylor for production, I'll assume that at least Indy's line has been developed to block for the run.
I'm glad for both of them as players and as men. They're both in a situation where they have a better chance to thrive.