Treasure Fleets is 100% determined by where you spawn in the homelands. If it's not on the east or west side of the continent, and you don't capture a port, good luck.
Otherwise, you don't really need luck.
It's not just where you spawn, but which direction you head. Like in my current game, I had a good antiquity where I had both east and west covered (although my production centres faced West). But there was just... no treasure. On the entire island chain between the continents, not one treasure resource. So I was already floating a settler out that way, but didn't really have anywhere good (there weren't even any spots with decent resources to get a home base.
I was slow to trot him around, and by the time he actually reached land with treasure, those lands were getting filled by others.
On the flipside, if I sent them and troops the other way, I just had one IP to clear out for a 2 treasure spot, and then there was some land on the continent with another 5 or 6 potential. But sadly I just didn't scan that way as quickly, so by the time I actually got out and have some city spots there, I'm going to run out of time, I think. I'll probably be able to eke out enough to get the first tier, but I'm definitely not getting the golden age.
It's still an interesting challenge, in a lot of ways. Settling the frontier, fighting wars in the homeland, etc... Although maybe next time I just need to make a bigger push militarily, and settle the new lands by force.