I'm just catching up with the World Team Trophy events. It's essentially more like a fun competitive exhibition. It seems stressful for a lot of skaters who either had nerves or else they have had trouble pacing themselves after Worlds.
Karen skated so well at Worlds and made an impression, it seems to me that she should have pulled out of this event and focused on a vacation and then preparing for next season. U.S. fed should have given Amber Glenn the opportunity to compete at WTT. Many feds mixed it up with sending different athletes for WTT event, which makes a lot of sense.
My impression -- just guessing here - is that the powers that be see a lot of up side to Karen's skating, while they hope that the challenges that hold her back can be met with only minor tweeking. This gives her higher potential than Bradie or Mariah, who seem to be maxed out. Alyssa appears to be a long shot at this point.

Amber is not yet regarded as a top-rung contender, but who knows what a year will bring?.
But it looks like Karen still has the Achilles heel of trying to overcome nerves and self-doubt. It's a difficult sport, with the mental and physical aspects highly complex and stressful. Unless athletes are able to relax to a degree and make the nerves work for you, mistakes easily happen. Ice is so slippery.
I wouldn't say that either Bradie or Mariah have 'maxed out.' I think that Karen has perhaps more superior aesthetic skills that the other two ladies. Technically, all three can tend to have issues, especially if they can't control their nerves in high pressure moments.
Amber has the 3-axel weapon, and she needs the opportunity to put it out there in a less high-pressure situation, which WTT seems to be made for, IMO. Also, Amber has very good musical interpretive skills, though some tend to not give her credit for her aesthetic talent. Mariah has improved tremendously, but she was under a lot of heavy pressure at Nationals this year. I blame U.S. fed for placing a bit too much hype on Mariah's shoulders, because they didn't reward her when they should have at 2020 U.S. Nationals, in her breakthrough performance. They were still fixated on over-rewarding young Alysa Liu, who even then had a tendency for URs on some of her money jumps (which often were ignored). Now, getting used to a different body, Alysa has to relearn her jumps. Alysa performed well at Nationals in January, but it's clear that there's a lot of work ahead of her to be able to get the jumps back that got her recognized and over-hyped.