An ISP (like one that starts with the first letter of the alphabet and ends with a common abbreviation for an explosive compound) might not think it’s worth coming out and marking their fiber lines when you call the city’s 811 number to mark utilities before digging for a project, like a fence.
If that fence ends up cutting the fiber line when digging a post, the company installing the fence can submit a ticket through a different portal than you as an actual residential customer of the ISP can, and that ticket probably gets responded to well before your attempts to contact them and request a call back because they are always experiencing a high volume of calls.
They’ll never admit any negligence on their part for refusing to mark utility lines, and you just have to remember where they buried the new ones, if they ever came back out to bury them instead of just leaving them aboive ground and flailing around.
Sometimes they even try to charge you for fixing the fiber line.