People tend to forget that both Morris and Staley would often leave Reeder as the only ILB on the field. On many of those runs it was because both DCs played a light box so it's not surprising they exploited that aspect of the defense. You can also direct blame at the DL if you are so inclined. More than was necessary, both DCs played their defenses to take away the pass and basically invited the run. So IMO it's not surprising when the only ILB is out of position to stop the run. Where were the SS and OLBs replacing the other ILB?
Reeder was an UDFA and as such he's played well beyond his draft ranking and why they couldn't tender him (with original draft). I wish him well (as long as he stays out of the AFCW). There is no doubt in my mind he will be a starter somewhere. Like Goff he was caught in a scheme that did not play to his strengths.