Because the orange style is not from the same "pack" as the blue styles.

If you observe the pattern of DK, we had the original couple of blue styles from years ago. Then we got most of the rest of the remaining skills during its class refresh. But the final two skills to "complete the pack" were reserved for Gold Coast Bazaar purchases. If you do all of those things then you have an entire blue "pack" of DK skills.

You will likely have to wait for the Arcanist class refresh to get the majority of the blue skill styles. Otherwise, you can buy two more from the Gold Coast Bazaar. The orange pack, like the Celestial Sorcerer style, are not meant to articulate with that "pack", they are more one-offs if you happen to find them interesting on their own.

Hopefully this answers your question.

I would like it if the re-rolls were weighted so we have a very low chance of getting the exact same challenge again.

It would also be welcome if "easy challenges" rerolled to "easy," and "hard challenges" (like a trial) rerolled to "hard." But I can see all sorts of issues with this, first being, how to define easy and hard for this case?

Added: yes, increase the number of possible challenges. I get this was the first round, and that's cool. But the endeavor lists must still exist! LOL.
Not quite copy/paste, but close.

BUT: for those, I really wish they'd spread some stuff out. Like, instead of "Public Dungeon in Wrothgar," make it DLC Public Dungeon, or Ebonheart PD, or something like that. So 1 or 2 PDs in one zone don't get absolutely slammed.
Same with World Bosses. Make it "Wrothgar and W. Skyrim World Bosses" or whatever. But spread out the crowds a bit.

And the "Kill X fire atronachs"-type challenges. Spread those out too. How about "Kill x atronach of any kind?" (I understand they're coded differently, but the endeavors had "kill chitinous foes" so something like that. And make it a reasonable number. 150 fire atronachs is a long time in The Forgotten Wastes (for example).

I think they're generally ok, but I would rather have more of a variety of tasks and not have to repeat each one numerous times. Doing the same thing over and over again can quickly become boring.

I'd rather see more than 5 tasks that can be repeated fewer times. I ended up rolling some highly specific ones, like harvesting 15 runestone nodes 6 times, which was more time consuming than challenging.

I feel that if we had more challenges (and all of them didn't need to be completed as much) we would have a variety of things to do and more of them would be passively completed. I wouldn't have thought to collect 90 runestones in my regular gameplay.

The free Tome path gives comparable rewards with less work. Most of the daily login rewards were kinda junk.

The better to part from your actual money, my dear