Comment Re:Is it the company's fault? (Score 5, Informative) 90
Many people who carefully designed such redundancy later found it gone due to mergers and acquisitions. Lumen has built one of the largest telecom companies in the world through M&A. So for example, you might have built your redundancy by getting links through Qwest, Savvis, and Level 3... all of whom are now part of Lumen. Over time, those links get "re-groomed" into the same fiber (DWDM may mean your "redundancy" ends up as just different wavelengths in the same strand).
It turns out to even be hard to hold anybody accountable, because contracts weren't written to say this can't be done (e.g. a contract with Qwest didn't say "and you can't carry this in the same physical route as Level 3")... and even it had been, custom information like that doesn't fit into the cable map databases and so doesn't filter down to the techs making design and change decisions years later.