Re: "While there's a bit of cost to set that up, it doesn't cost much."
bar any unfortunate backhoe you're sailing in clear seas, money dropping like rain every second.
Sadly not true. So there's up-front costs, like civils to construct ducts, lay fibre, buy/lease land for regen sites or PoPs, negotiate wayleaves etc etc. Then for wet stuff, landing stations, backhaul, licences, marine surveys, cable, cable ships, wet cable stores etc etc. Some of that translates into ongoing costs, ie property rents, space, heat & power, hardware & software licences, operating licences, staff costs for selling & supporting services, legal costs.. And maintenance costs.
For the wet stuff, that can happen when seas aren't clear and one or more cable ships may be needed to find a fault, yoink the cable up, repair it, and replace it. The cable laying and maintenance ships are highly specialised and expensive. Cable owners pay into maintenance funds so ships and crews are available to try and meet the 99.999% SLA's sales sometimes sell customers. Which may involve sailing a long distance in bad weather to sort out. During the .Com crisis, funding those ships got a little challenging and there was a risk that some ship operators may go bust.
But it's not cheap to operate a large network, and it's just Sod's law that as route miles increase, so does the likelihood of outages. And if market forces conspire to create a perception that bandwidth should be cheap (or free), then something has to give.. Which is often support and maintenance activity.