Actually, it was mostly twofold. One, Russell and Randle were one and singers, their bodies aren't that mature and the brass was getting their bodies used to playing against grown men in a much longer season with less rest between games. The rookie January wall and sophomore wall are what happen when you overload rookies early on. Look at Russell's legs last season. Look at how much trouble he had fighting through picks on defense and keeping defenders on his hip on offense.
Second, for Russell, there was a lot of concerns about his work ethic. Check out Pincus' posts for more detail. Scott and the front office wanted to light a fire under him. Conversely, with Randle, they wanted to slow him down down. The coaching staff saw that he was favoring one leg, which was a recipe for recurring injuries. Recently, Kupchak noted that Randle is finally confident in both his legs now. It shows.
There were very good reasons for last year's minute management. Lakers front office have made mistakes, of course. Minutes were not one of them. Likewise with Scott. Obviously Scott has failed to adjust to today's basketball meta. But his work in developing Russell's work ethic will be invaluable, making him understand that he can't just take his future in the NBA for granted just because he was the second pick and is on the Lakers.