Maybe the game is trying to tell me I should take cheap diplo wins when I have the chance.
That's a matter of choice. Winning on the first vote is only possible if fortune lines things in your favor. Like, a top rival who has already ticked off the rest of the galaxy. You still have to be one of the two largest civs to be nominated, though. So it's more like "luck is the result of thorough preparation" than being handed a victory on a silver platter. If opportunity knocks and nobody answers, what good does that do you? Likewise, why let good fortunes and rare cosmic alignments bring a premature end to an interesting map?
I can't blame you for pursuing a higher challenge. If you fail, I'm sure it won't be the first loss you've had where you could have had a diplo win and passed. I know I've racked up plenty of those. In fact, my record with even the Mrrshans is better than 50% if we discount losses where I passed on a winning election.
I still play on Hard sometimes, too. And still lose.