It is always a political choice, but it seems preferable, to me, not to hold a referendum at the same time as an election. It is possible to do that where I am, in Quebec, in municipalities. It is open to them to hold certain types of referendums at the same time as a municipal election. It is open to them, but they don't do it. I have seen one municipality in the past that wanted to do this. Ultimately, it decided it was too complicated and decided against it. I think that was a political choice.
Might there be subjects on which the government would want to hold a referendum and an election at the same time? It's possible, but myself, as an election administrator, I can assure you that I prefer it to be separate.