When connections are leased, the cost of a physical fiber expansion may be prohibitive. You may also be confronted with lack of availability and long lead times. Some suppliers offer “deployment priority” but this often comes at a high price. To top it all, some suppliers may even charge excess construction charges if there is no or restricted capacity.
If you own your own fiber assets, you may be confronted with the practical aspects of the additional infrastructure deployment. A number of years ago, a single fiber pair looked more than sufficient in terms of capacity, many direct burial cables with a limited number of fiber pairs were used.
Adding capacity here means re-trenching which may be expensive, disruptive and is often subject to road traffic management and way-leave agreements. Likewise with ducted systems, these are often lacking accessibility, may have collapsed over time or are often overfilled already.
When cables are routed through buildings, for example above suspended ceilings and through risers, with the added complication of having to breach fire-stops etc, it is obvious that deploying additional fiber can be a very challenging and disruptive prospect.