Some bikes are just more trouble to overhaul than they're worth. I agree with USAZorro - a compromised frame is an automatic death sentence in my little shop of horrors.

I'll usually strip rigid frame mtbs if they are in too much disrepair, as they will never sell for enough to cover the aggravation in putting them right.

In general - If I can't make a clean, safe, presentable, and reasonably profitable bike out of a hulk I drag home, it gets stripped for parts