This was the way Turnbull's PMship was always going to go. The Lib party is a lot more conservative than it was when he signed up - Howard and Abbott spent a lot of time easing the moderates out. That's why he got rolled the first time round - too willing to accept climate change is real and something should be done about it. The lib party room didn't want the leather-jacketed socially liberal technologically minded attitude that Turnbull projected when Abbott was PM. They wanted the approval ratings that Turnbull had, but the policies that Abbott had (with fewer self-inflicted gunshot wounds to the foot...). The lib party room wanted Abbott in a Turnbull mask. When turnbull challenged, he had to sell out everything that'd ever made him popular in the electorate in order to win the vote in the party room. And even THEN it didn't appease Bernardi, or Abbott, or the rest of those flakes, and when was PM and changed his tune on everything he'd ever believed in, surprise surprise, he's not as popular any more.
Truth be told I'm not sure there was a winning hand for turnbull to play, not if he wanted to be PM. He could have said to the lib party room 'if you want me to be leader then it's my way or the highway on policy' but then they would have replaced Abbott with Hockey or Bishop or someone and probably lost the election anyway and he'd never get a go. He could have let Abbott lead the party to the election, and the libs would have lost in a landslide, which would have meant that they'd lose a heap of marginal seats which would have weakened the lib moderates even further because lib safe seats tend to be in conservative electorates and have conservative MPs. The party room would have been reduced to a handful of conservatives in safe seats, and that mob would never ask Turnbull to lead. But instead of these options, he chose to bargain everything just to get his backside in the big chair, for a little while. Lose-lose for him. .