The reasons to do FTTC/VDSL/vectoring instead of FTTH are obvious: they are about capex (cheaper) and demand (supposedly there isn't any). But when BT, DT and the Coaliton in Australia gamble on FTTC, it creates a family of elephants in the room. If you want to do FTTC, that's fine, as long as you acknowledge that it has a few issues.
It may save on capex, but FTTH saves on opex. And if FTTC proves insufficient, it risks being a 'regret investment'. It is going for the short term, instead of the long term. Put differently: the greatest benefit of FTTH is its opex savings of around 20%.
Further, vectoring is still quite experimental. It is completely unclear what the real-world performance will be and which share of the lines it can be applied to.
Doing a bottom-up assessment of the number of devices per household and the usage per device may render a picture of the demand side, but it completely ignores innovation and unexpected use cases. 4K is moving faster than previously expected and gaming may be a major growth driver.
To be fair, ongoing compression is relevant and also the fact that we are moving from a downloading to a streaming world. And streams are offered at a certain fixed rate. Making the access network 'faster' doesn't help. And the access network isn't the only bottleneck in the system.
3. Quality of service
Any bandwidth will suffice for anybody, as long as we don't care about QoS. As demand rises and networks aren't upgraded at a similar pace, QoS will go down.
If one could isolate the 30% (or whatever it is) that would be willing to pay for a gigabit, it would be easy to roll out FTTH there, and FTTC everywhere else. Only this doesn't work for several reasons: people move every 7 years or so; building nationwide FTTH in any country will probably take 10-20 years; and the 30% that needs a gigabit changes every month, so in reality it is probable closer to 50% (or whatever it is). Compare Cisco's statement: "the top 1% is actually the top 5%".
5. Business model
Traditional telcos are rooted in scarcity. They will upgrade not ahead of demand, but somewhat behind demand (in such a way that complaints are controllable). It is their game to minimise capex in order to maximise shareholder remuneration. And capex peaks are to be avoided, when shareholders must be reported to on a quarterly basis.
Google on the other hand is rooted in advertising. Governments, like Google don't want bandwidth to be a scarce resource. Google because it wants to maximise usage in order to create advertising inventory, governments because of the economic, social and environmenal benefits of migrating online.
Both business models can be applied, but looking at it this way explains why others besides incumbents are getting involved.
FTTH is not about download speeds alone, but also about the uplink and latency. And if it's not GPON but point-to-point, it is also dedicated instead of shared.
7. FTTH has a lot of supporters
Governments such as the current one in Australia, Google, KPN (sees FTTC as an interim technology), challengers such as Free and HKBN, several cable companies, etc. prefer FTTH over FTTC for any or all of these reasons.