Before fiber a lot of things were put into the ground with no thought how you would find it again.
I sometimes hire directional boring and excavation contractors and if there’s any doubt as to where an electrical conduit or natural gas pipe is, I opt for the hydrovac truck to minimize risk.
And of course there are marker posts that say "buried fiber optic cable do not dig".
Most cheap hired labor doesn't realize you shouldn't dig up the market posts and throw them in the dumpster on construction sites. Add a little bit of rain and suddenly the contractor showing up with an excavator that was told everything was properly marked, and can see markings in other places but not where they are digging, and disaster occurs.
Also soils aren't static, I've been on sites where the midpoint of a buried telecommunications cable had drifted over 8 feet from where the markers were a few hundred yards apart. Just looking at the markers and assuming a straight line isn't a safe bet. Looking at the fence rows to the left and right of the cable and you could see a matching bow in the fence rows.