[redprince]

> lack drive and take longer PTO and their work isn't really that adequate.

People sometimes come to realize important things when they mature. This may include insights like "there's a life happening outside work waiting to be lived". Or acquiring a better sense where it pays to spend time and energy for maximum effect and where it is wasted.

> Blaming interns or junior engineers for simple mistakes, which the senior which also should have seen.

Juniors making simple mistakes really doesn't rhyme with the rest of what you said. Are they

a) Brilliant people, able to replace seniors while being paid a pittance for working their ass off?

or

b) Actually inexperienced and still have to learn a lot until their output has the required quality?

> Not training interns or junior engineers to become senior and be given more responsibility

Any junior waiting to be taken by the hand and shown the path to greatness through careful and detailed tutoring by colleagues I can recommend only one thing: Learn to learn by yourself. Fast. Your colleagues are busy with their own work and tutoring you very often has very little bearing on their current goals, compensation or career prospects. It is thus one of these areas where they have learned not to spend much time and energy. (Though some people have strong altruistic tendencies and/or find it satisfying to mentor and teach, but that's an intrinsic motivation which is either there or it isn't. When you run into someone like that: Lucky you!)

On a more calculating note: As you have let on that you think juniors are viable replacements for senior while being cheaper, the seniors might not be very motivated to bring their replacements up to speed...

> we are all aware of the bus factor here

As an employee, that's generally not much of a concern.

> All the while where some really smart interns or junior engineers come out of prestigious institutions

I suggest you attempt to hire them. I wish you the best of luck!

> I am a senior engineering manager looking to take on interns.

Do it. It's going to be a valuable learning opportunity for everyone involved. Including you.