I think it's because on the surface City have got a fantastic team full of class players that it's difficult to see a pathway into the team for talented youngsters. Please don't kill me but I was one of those people who used to say Foden needs to either leave or go on loan for his own good because City had KDB and both Silvas ahead of him at one point, but Pep and Foden proved I completely underestimated City's ability to integrate their youth prospects. Bobb appears to be on that wonderkid level of prospect, so I have no doubts he'll find his way into the starting line up sooner rather than later, and his obstacles are way less daunting than what Foden had to fight through.
At United, if you're half decent you're straight into the first team, as proven by Mainoo. Foden had to work extremely hard for his chances, Mainoo was thrown straight in there.