It's random. And it's different for each platform/region. It's been the weekly multiple times on PC/EU and PC/NA.

"But it's been half a year!", you say. So what?

There are 10 different trials that can be the weekly (3x Crag, 3x full DLC, 2x mini DLC, 2x 4-person arenas). It's been 27 weeks since Update 22 hit console. What are the chances that a specific trial out of a pool of 10 trials never come up after 27 weeks? Answer: 5.8% Sunspire specifically never coming up is improbable. But far from impossible.

And what are the chances that, after 27 weeks, there is some trial (not necessarily Sunspire) that never appears in the rotation? Answer: 45% So you've pretty much got a coin-toss chance that there will be something that, after 27 weeks, wouldn't have appeared. In other words, what happening is here completely normal.

Change the words around and imagine someone saying, "27 runs, and I still don't have a vMA inferno! And I just got ice staves two runs in a row!" And then someone else comes by and says, "Haha, I just got two infernos in a row within my first 10 runs!" Well, this is no different than that.

TL;DR: It's just a roll of the dice. Now, you could argue that random selection isn't the best way to go about selecting the weekly. And I would be inclined to agree with that. But given the current system of random selection, what you see is perfectly normal.


Edited: For clarification and to include calculations, as shown below:

• Probability of a specific trial out of 10 possibilities not appearing in 27 chances: (1-0.1)^27 = 0.058
• Probability of any trial out of 10 possibilities not appearing in 27 chances: 1-((1-(1-0.1)^27)^10) = 0.45