A practical drawback to premade cables is the need for a larger hole to accommodate the pre-attached connector. There's also a larger gap that needs to be plugged around the cable to prevent leaks into he wall.

My ordinary home-centre electric drill and an affordable ~7mm masonry bit lets me drill a hole in stucco large enough to accept bare cables with a very narrow gap to worry about.

Where are you finding them for that cheap? OP is talking about 20GBP for a run of fiber. If I look at, for instance, Ubiquiti their direct attach cables start at $13 for 0.5 meter cables.

I was looking at patch cables. Ubiquiti's start at $4.80

Right you're still going to need a module at each end, that's what really drives up the cost compared twisted copper pair. That means either direct attach cables (starting at $13 for a half meter) or standalone modules (starting at $38 for a pair of 10G modules).

But that also applies to a spool of fiber, and I was talking about the specific cost difference between fusing and premade.

The price of modules was built into the first post mentioning fiber up here: https://news.ycombinator.com/item?id=41891559

The worry was that the actual fiber would be "stupid expensive", and nah it's fine.