De Boer was approached recently by the Russian club following the sacking of Unai Emery but turned them down.
Instead Spartak appointed director of football Valery Karpin on a caretaker basis until the end of the season.
De Boer told De Telegraaf newspaper: “My work with Ajax is not finished.
“There is still a lot of growth in this team and at Ajax I have fun every day.
“Also my family played a part in my decision. I have three beautiful daughters and a beautiful wife. She owns her own shop where she has a lot of fun. Was I supposed to tell them ‘we are going to Russia?’
“No. Money is not the most important thing. Six million euros net per year from Spartak was a lot of money but that’s me.
“I am busy with something at Ajax and I am not done yet. Happiness should always come first.”
De Boer, 42, has led Ajax to back-to-back Eredivisie titles since taking over from Martin Jol in 2010. His current contract expires in 2014.