Man. I am of two minds on this.
1) Shang-Chi's gross should not be held against it. If anything, I think it speaks to how big a commercial (and critical) success it was, since September 2021 was still the dregs of COVID. It was also before they'd figured out that "theater exclusive for 45 days" was bad, IIRC. It was #1 in the box office for 4 consecutive weeks, according to wikipedia.
2) That said, I've always felt like Shang-Chi was a weird choice for the MCU, or rather a character in a weird spot. In the comics he barely has any connections to other characters. I've seen him pair with Black Widow, Daredevil, Iron Fist, Luke Cage, and once with Spider-Man. Only one of those is in movies right now. He certainly doesn't have a rogues gallery to call his own.
Other than having a decent origin story (which we've now seen), there isn't much. He's Iron Fist without the powers, cool costume, relationships and mythology. They basically gave him powers and Iron Fist's mythology (mystical cities, dragons). He still has no natural relationships to lean into (unlike, say, Iron Fist with Luke Cage or Daredevil with Punisher or Spider-Man).
Also, we still don't know - and there are no strong comic book theories - what his post-credits was alluding to. Presumably it may have tied into Kang. But they had him walk through a portal to meet 2 Avengers because there wasn't a more natural way for him to meet anyone.
So if Shang-Chi 2 never happens... then I guess that's ok. Maybe they're admitting that not everyone needs a trilogy (Ant-Man sure didn't, as he's never held a sustained solo comic run) and they didn't have any real plans for the character. But it's bizarre that they haven't tried to give him a cameo or anything. He's well-received enough to where people actually want to see him, and haven't, and 3 years later it's gotten a little weird.