Other lands, other conventions. I can only talk about Germany. Here the landlines are (almost completely) underground and 90% of them are owned by the one and only sucessor of the former state-institution "Deutsche Post"...the almighty "Telekom". In the U.S. you know them under "T-Net / T-Mobile" ,the "magenta giant". An isp is literally only that: an internet-service-provider. So here an isp is dependend on the work and infrastructure of ONE lineowner. Sure they are others, but they are in a minority holding accessable landlines "for everyone". So if the line is shortcircuited or even damaged, it literally takes weeks until the line is fixed. Even if you just want to move from one appartment to the other within the same building, it takes 3 weeks in average to switch the landline, because...because. Bureaucracy rules!Worked for the largest ISP in my area, hated it, but that's a different story. I do know that most of those "faulty/old landlines" at least as far as the US is concerned, are predominately POTS lines these days, with the occasional crappy aDSL service, but even that is dying rapidly.
However, faulty lines do occur regularly, usually from the pole to the home, or from the node to the pole. Your ISPs will, with some level of complaining, replace the pole-to-home run. More often though, it is the node-to-pole lines that have been there for 10, 20, or 30 years. The insulation on these typically crumbles when handled and even birds and squirrels don't like to get on them. Your ISPs hate replacing these however, as they are typically long runs, which means lots of cable, as well as not just taking you offline while the replace them, but an entire neighborhood.
There there is the matter of the nodes themselves. You've likely seen these, little, greenish, locked metal boxes, like the ones the electric companies use, though usually smaller, often not on a concrete slab, and what's in there? Mostly routers, usually expandable routers, a bunch of cable terminations, and...
Mice, rats, gophers, chipmunks, nesting materials, and water. Yeah, these things get to be straight up disgusting. I've cracked a few of these open and discovered a rat king. Yuck.
Getting your ISP to maintain these though... you'd need to get all your neighbors complaining at the same time, so you may need to have a neighborhood meeting prior to making those calls, so everyone can get their story straight at the same time.
Can't say if it works the same way on the other side of the pond, but I imagine when it comes to complaining, y'all could teach us a few things. ;-)
Finally, when it comes to the cost of a fiber run... yes, if you, individually, call your ISP and say "I want fiber, and I want it next week.", yes, your ISP is going to tell you "$10k, up front." However, there are ways around this. Again, talk to your neighbors. You might not want to soak a $10k bill, but 30 or 60 people might not balk at an extra $14 a month for the next year. See, thing is, your ISP's, especially here in the US, are just miniature monopolies - however, they are precision-crafted by the finest lawyers, to ensure they just skirt around the Truman Antitrust Act, and when they do get right on that line, they're greasing politicians with sums of money Bill Gates would actually miss. Your money, which they recoup from you, in the forms of strange little fees the law makers ensure they are allowed to pass right back to you.
As "our" chancellor once said: "Internet is the undiscovered country". Still we have places in major cities that are not sufficently provided with G4, hence 50MBit/s landlines (I have to live in one of these blind-spots, till I get my new job, hopefully within the next 3 month, but it's a stable 16MBit/s connection without any dropout the last 5 years, so I don't complain( so much)).
One other thing: "We" germans call ourself (but never commit it) as "the masters of complaining". We WILL complain about the tinyest things but heck, we don't want to get our fingers dirty. So I cannot count on my neighbores.