Not just that, but the Liberals presented Turnbull as some sort of masterful IT expert on the extremely flimsy pretext that he made a shitload of money flipping an ISP two decades ago.
He has a slightly better grasp on some areas of technology than the average person perhaps, but certainly no more than the absolute bare minimum any communications minister should be required to have.
I agree that his actions as communications minister that contributed to this were horrible, but being given communications minister was essentially a punishment for crossing the line.
(1) The NBN falls under the portfolio, and the government knew they would have to deal with controlling the ever increasing costs of the program, which were hugely underestimated by Labour, and
(2) The person in the role of Communications minister would take the blame for the public realisation that the costs were going out of control and had to be cut.
(3) Any cut would result in a poorer NBN, because that's what cutting costs when you're building any product/service does.
So he was essentially handed that flaming pile of dog shit by Abbott, probably to lower the chance that Turnbull would ever be able to wrestle back power.
Turnbull's solution was to get the private sector to pay for a part of the network (FTTN instead of FTTH). So, costs would be managed, the 2020 target was still reachable, and it leaves the NBN open to improve the network to FTTH later on.
What could Turnbull have done better?
The bigger problem of the NBN is its business model, which charges Telcos for bandwidth on a total downloads basis rather than on a % use basis. This is what causes the poor service of the NBN. This could have been dealt with by Rudd, by using a different model for the NBN, as discussed above, but Turnbull couldn't do anything about that.
He has a slightly better grasp on some areas of technology than the average person perhaps, but certainly no more than the absolute bare minimum any communications minister should be required to have.