Here's my "out of the box" take on what happened last year. I have commented on this before, so its not a new revelation, just not in this forum. Watching camp from day one, Isaiah Pead was "THE GUY" getting the majority of all the reps. Richardson didn't practice the first 2 weeks of camp, due to a hamstring strain. They were limiting Jackson from the outset of training camp, giving him reps at the start of each session, then immediately going to Pead.
Pead also got the lion's share of the work in the 1st two Preseason games, all BEFORE Richardson made it back from his injury. IMO, not only were they trying to get Pead as many reps to "catch up" from missing all of the OTAs, he was the only one getting the reps.
When Richardson finally got back on the practice field, it was OBVIOUS his legs were fresh, and it was like everyone else was in slow motion. He was lightning hitting the holes, and yes, he did indeed AT THAT POINT look like the better RB. Pead fell victim to "camp legs" and never recovered. Not saying he was any different than he had been, but the difference between a fresh Richardson, and ALL of the other RBs at that point in camp was noticeable.
Now, fast forward to the start of the regular season. Richardson is now firmly entrenched in the backup role, with the "bellcow" veteran leading the way, there just wasn't going to be opportunity for a 3rd RB to get the reps, be it in practice, or on Sundays.
Throw in what we now know, of his "off field" issue last year, it further explains why he fell off the map.
Now moving forward, by the mere fact that the guy who they were committed to feeding the ball being gone, and the guy who did in fact has the benefit of being the "incumbent", Richardson inherited the "starters" label for now. But given the overall youth and inexperience of the entire RB corp, and that they all have their own strengths and weaknesses, each and everyone of them will be given their opportunity to contribute.
INCLUDING PEAD, who is STILL sharing reps with the 1st unit offense.