So if I work at company A as a junior and get paid the same salary as a senior at company B, why is it bad that my expectation is to keep getting paid at the le

So if I work at company A as a junior and get paid the same salary as a senior at company B, why is it bad that my expectation is to keep getting paid at the level of A even if I want to switch jobs? Or does your comment apply to fresh grads? Because then your comment would make more sense to me.