Even when you express it clearly, many juniors won't understand and will feel frustrated. Some things can't be taught and must be experienced. Every junior developer must work on a crufty legacy codebase to develop understanding and habits for writing maintainable code.

Large companies pick experienced internal transfers for shiny new projects and hire externally for unglamorous legacy systems. Since all new grads are external hires, they end up starting out on legacy systems.

I recommend that junior devs start out at Amazon. They will learn a lot of important things in a year or two: the pain of technical debt, the value of automated tests, the pain of production issues when you're on call, that working overtime is not rewarded and does not solve job insecurity, and that switching companies is a great way to get more experience and earn more money.