"I have a young daughter and I'm getting married in January. So I just thought about my family and, in all honesty, sticking in the AFL as long as possible, and – it sounds horrible – but to try and get as much money as I can for my daughter as she grows up," Hartley said.
"That's where we're at, unfortunately. I loved my time at Essendon and I love the club, but the Hawks came along and gave me a little bit longer."
With the Hawks having a talented backline, Hartley concedes the hard work is ahead of him.
"There are a couple of big dogs here already, but I'll back myself to have a good crack," Hartley said.
"I'm happy to do whatever the team needs. If I start in the VFL, I'm happy to start there, and hopefully I'll just work away, chip away, and get the form up."