It's the fine line when the pressure is on. He's been a decent player, but we were going for 4 trophies in Klopp's final year. The pressure is just different, particularly with injuries. If we were solidly Top 4, humming along in the CL, Cody is getting up to speed, and Klopp is just getting started, I don't think too many people would be bothered by his impact.
When you think about the fine margins that determine how many major trophies Klopp can win, the pressure really is on. Add to the fact that Salah and Jota have been injured, and you're expecting Cody to step in. He's played in Europe every season, played well over 150 times for PSV, been here a year, and scored at the World Cup. It's not like he's a kid who's just breaking into the first team. So naturally, when we're outplaying City at 1-1 or trying to see out a rare FA Cup win at Old Trafford, you're hoping for at least an Origi type hero moment. Instead, he doesn't really do much. It's not like he's cost us matches, but he just hasn't had the moments for getting us over the line in big games.
It's both the blessing and unfortunate circumstance around big big pressure games. Origi is a hero forever for his big game moments. If Cody scores the winner in the PL (like Darwin did) and helps us overcome Atalanta and Benfica/Marseille on the way to the EL final, he'd be loved. At the same time, when we desperately need a moment of magic in a massive game (like City), and he doesn't really make an impact, it stands out glaringly, especially when compared to Salah/Nunez/Jota/Mane/Firmino/Origi. Diaz gets some stick for poor end product, but his work rate and dangerous dribbling ability tend to stick out (see City even as he missed multiple chances).
Cody just hasn't been able to "wow the crowd" and have his moment yet this season. But there's still time.