There are a couple reasons for this:
FNO case:
1. Fibre is expensive to install. Economies of scale on FTTH deployments, and relatively low churn, mean that the unit price to deploy is much cheaper than some businesses - We've had builds in excess of 150-200m just to light a single business. This costs R150-250k (Planning, Wayleave, Civils, road crossings, hardware etc). Trenched fibre costs are anything between R600k - R1m per Km, depending on area.
2. Contracts are part and parcel of life. They ensure that the supplier isn't throwing the above money away in building something for a non return. They protect both parties, and a good contract is only necessary when something goes wrong. Most importantly, they protect the client by binding the supplier to a certain level of service delivery (uptime, quality, mean time to repair etc). Extending the term on changes is a relic of older contracts some ISPs have with their upstream, but is mostly gone now.
3. Fibre is expensive to maintain. 24/7 support, SLA commitments and more mean that you need to have an always on NOC and maintenance crew to fix breaks. And If your business needs internet, you need an SLA - downtime costs money, no matter which way you cut it. We've reported line breaks at any hour and had our MTTR met. The larger residential FTTH companies once again benefit from scale in maintaining their networks, but none of them offer less than 72H MTTR. Smaller companies sometimes make you wait days for a repair. Then the ISP also needs to be able to provide support and NOC staff to support your service.
4. The infrastructure deployed in South africa is world class and is mostly trenched - it's cost a pretty penny and there are no businesses piggy backing off consumer grade networks, most often, it's the other way round.
ISP Case:
5. If your service provider doesn't have redundancy on their network, they should not be supplying you business fibre. The only real risk should sit with businesses who chose a single last mile - there's a risk that it breaks and in turn, there's an SLA that says how quickly it's repaired. From the POP backwards should always be fully redundant.
6. Three years ago, 1 Gbps enterprise level switching was the norm. Then everyone raced to 10G. Today some ISPs operate 40G and 100G switching. This means constant re-investment. So network investment is not static, it moves with the business (and carrier kit is expensive).
I could go on and on. What's promising is that now that some networks are maturing, broadband services are beginning to be offered on those lines. This should see a reduction in costs as well as a sharp increase in speeds becoming available to businesses.