In a study by J.J. Zachariason, 54 running backs were drafted between Rounds 7 and 15 behind a top-12 running back from 2011-2017. Of those, 32 offered three or fewer top-24 finishes. This means a majority of the time you select a handcuff, you will have three or less useable weeks. That also includes games in which they score a random touchdown, or take over after a mid game injury when you would have left them on the bench.
Taking Alexander Mattison on a team with Ezekiel Elliott allows you the chance to stack hoards of receivers and an elite tight end, with the possibility of starting both Mattison and Elliott should Dalvin Cook get injured. That’s a team others cannot replicate or compete with. Drafting a handcuff to your own running back takes the possibility to benefit from chaos off the table. You can derive only benefit at your own expense.