Only liberal-minded politicians will presume that Labor would take over, with all due respect. Do a good job and Labor would not have a chance.
Also, referendum votes can be skewed. They do not represent the will of the people, but a quieter form of mob rule.
Eventually a Labor government is going to win an election. It might take twenty over twenty years as it did in the Menzies era, but eventually it is going to happen.
And, yes, referendum votes can be skewed. That doesn’t change the fact that they are an accepted way - indeed, at time, the only constitutional way - certain things are done in Australia. I think people outside our borders often don’t understand why the referendum is such a common tool in Australia - it’s because it’s what the people who wrote our constitution decided to put at the core of that constitution. Even if you think they were wrong, conservative governments tend to follow constitutional rules and that’s the one big one here.
When Abbott made his decision about a plebiscite, he might realistically have been hoping for as many as three or four terms in office for a Liberal/Coalition government - but four terms is rare - and Labor would have sought to make each election one fought almost solely over same sex marriage. It would have become the most important issue in the country’s political process - and that would have been a ridiculous situation. Getting it out of the way so the government could actually govern was sensible.