I don't doubt that it happens; just not for the reasons you ascribe to it. It's probably just the fact that the wiring boxes are usually a complete mess and totally inconsistent from job to job. The contractors get paid by the job, so their attitude tends to be "fuck it, rip it all out and make it work so I can get to the next job".
Perhaps but they're doing it in a Comcast/Verizon truck, wearing their uniform, talking about that as their company with no mention of being a contractor, and in at least two of those cases they specifically went to extra work to remove the cable even though it didn't come in the same box / conduit as the new fiber. That was actually why I first heard about it: a coworker mentioned his surprise that the FIOS installer spent the extra time removing Comcast's cabling all the way out to the street after finishing their install.
