If BT improves the exchange to enable, say 21CN architecture as they will eventually have to do then they will be able to offer faster packages which most people would upgrade to in market 1 exchanges to get a better service. The better service costs more, returning more money to BT.
In some market 1 exchanges there will be large growth as villages are expanded to provide housing, increasing the population and demand for services. As urban sprawl is limited from towns and cities, commuter villages that are served by market 1 exchanges can be seen to be a good revenue source for BT etc to upgrade the exhanges that serve them.
There are remote places that will require large investment, proably goverment if they will see improvements, Market 1 really should be divided so that the final third can be shown as to what areas are a good return for investment and others that will need public funding to provide access to them which will proably be a gd few years down the road.