1 - Code review is inefficient at catching subtle bugs. You're not paying the same attention when you just read the code vs when you write it and test it. And even if you're particularly good at it, your colleagues might not be.

2 - Even if junior programmers exist, they don't write all the code produced in a company. They're usually in teams with more experienced people. You probably shouldn't hand the keys to juniors and leave it at that, if you want to get stuff done.