I suspect this is my situation as well, although the conditions in the first sentence do not fit. We are on the maximum length of copper. Due to variations in weather, I also suspect the copper may not be in the greatest of shape and the insulation of it may be compromised.
Ia any part of your line up in the air on a catenary wire? Overhead cabling, even in good condition, is affected in poor weather. I used to have customers calling in for support laugh if I asked "Is it raining where you are?" but I've seen the phenomenon so often that I'm in no doubt that it's real.
DSL pushes the boundaries of what it is possible to stuff down a copper twisted pair that, crucially, is bundled without shielding with lots of other copper pairs. When DSL was first being mooted I remember a lot of engineers saying that it would be impossible to get the 2 Mbit of ADSL down a copper pair that was typically thought of as having about 6kHz bandwidth, and noisy at that. It's no surprise that if you alter the conditions then what will successfully pass over the line varies.
Yes, it is a catenary copper wire. From what I gather from others who have different lines in the same municipality, is that mine is worse so I assume a catenary wire that is in unacceptably poor shape.
However, there might be something else going on with the line, as the DSL modem has been replaced three times this year. At some point, it stops connecting to the line...
Of course, the other shady practices of ISPs that Vince described are well known to happen here in the GWN. Some of which are plainly written into the contracts that ISPs provide, although I feel like I am the only person who read that far (even I did not read the whole contract...).
Maximum return on investment = getting away with sub-par service
One can't entirely shovel the blame on the ISP's greed. Back when I had to make the decisions whether it was commercially viable to establish a new point of presence somewhere, and hence had to pay for cable laying work, it cost about £150 a metre to trench and lay [direct burial] cables/fibre in a soft verge, £250 a metre to lay cabling under a pavement (sidewalk), and £500 a metre to lay cabling under a metalled road (prices circa 2000AD).You can nearly double those prices for ducting. That adds up very quickly. A back of envelope calculation says that just to get fibre/cabling from a mid street cabinet to every one of the roughly 50 houses in my road would cost £92,500. That's without backhaul anywhere. That's £1850 per house (2000 prices) before you've blow any fibre or paid for any electronics.
Add hardware, backhaul and operating costs and it's pretty easy to see that the ROI isn't very attractive. If you're competing with an incumbent who wrote down their street plant (buried cable) costs years ago and hence can set unrealisticly low prices you're stuffed.
Ah, the part I did not think to mention is there is no real investment. The federal government has provided a billion dollars to pay for high speed rural internet access, with a minimum speed. The provincial government has a similar scheme, but I am not aware of the dollar amount. We are way below the minimum mandated speed. There is no ombudsman or bureau to complain to. The ISP has certainly collected the money, but not spent it in this neighbourhood.
The fibre installation is not likely as expensive as you think. The fibre in nearby areas is a line up in the air on a catenary
wire fibre. Maybe such a fibre is more expensive as it needs to be protected differently? They are running it using the same infrastructure as used for their copper lines and for the hydro(-electricity).
The ISP has a monopoly in the area. The single company runs the phone system, the DSL, the fibre and 3G, LTE and the non-existant 5G... switching services does not include switching provider.
A few people who have waterfront property do have options. There are radio-based line-of-sight services available from the other province across the river. It it far
much better performance, but at a much higher cost. However, one assumes that someone who can afford waterfront can also easily afford expensive internet access. Then again, the performance per cost is better.
In reality, it is probably a combination of your assessment and my thoughts (and highly likely a dose of what the dwagon suspects).