No competent designer facing the uncertainty of the future would precisely optimize plant based on data which would be years out of date at the time of completion. Good designs and budgets include margins for error to account for the changes which occur over time and for the inevitable mistakes made by humans. This might be true in more densely populated areas. But spare capacity cannot provide a margin of error in census blocks where little or no plant is built because the data was out of date or the guesses were just plain wrong. Precisely optimized plant is unrealistically forward-looking for rural areas.
Designers also focus on system flexibility.
Lowest cost solutions, even on a long term basis, are not necessarily the choice of competent designers. In the plant design put forward by FCC staff, for example, copper based T1 subscriber carrier is applied below a breakpoint while fiber-based carrier is used above the breakpoint. Copper does not migrate gracefully to fiber, it must be replaced. Besides, no one is installing new copper T1 systems in rural America today except, in a few cases, on existing plant. The Act of 1996 defines universal service as an evolving level of telecommunications.