What is so wrong with marshall food?

my boy has been on marshall ferret kibble ever since i’ve had him, and he’s totally fine. he’s a normal, sleepy, floofy, energetic ferret. After joing this sub i always see people say that marshall food is bad. so i just want to know what is actually so bad about it, because my ferret has been on it his whole life and he’s perfectly healthy. thanks!

edit: forgot to mention, he’s on the premium ferret diet.