if you pay them better they won't leave. But you've basically said that even after training they are worth less than someone you hire in at first. This distinction is why people leave. You trained these people in the way you'd like them to work, Tailor-made to your processes but you still say they aren't worth the same as the people you hire-in. No wonder they leave and go some place where they've now been hired in without needing to be trained. If you don't value your own training highly enough to pay these people the market rate, what reason do you expect them to stay and work for you for?