Because those guys all get into games every year. Blackwood also played most or all of last year while injured. I recognize that sometimes goalies get to a point where they are always injured, in one way or another - I'm not certain Blackwood is there. Nonetheless, he had an obvious injury that needed surgery to repair.
I don't really see much need to parse how good goalie #49 is versus goalie #58. That's overwhelmed by luck. So sure, Blackwood has one of the worst SV%s over the last 3 years, but he's also played for one of the worst teams. He'll have a job somewhere next year, hopefully not here, but he'll play somewhere. I won't exactly be rooting for him but I won't be rooting against him either.
I hope last night is Blackwood's last game here. But he played well, so I don't see why he would be a big topic of conversation after the second period.