"I was pretty confident, particularly with the win in the Constellation Cup, that it would be possible to seek an extension of the contract but obviously the board thought differently to that," she told Radio Sport.
"This is the thing that's hard with coaching, you've got to be creating the next group of athletes for the next event as well at the same tie as winning ... I was excited by the group and the talent we had and that was on display in the Constellation Cup.
"It was looking quite good for the future but obviously I'm disappointed that the board haven't seen fit to renew my contract and they've made the decision to go in a different direction. At the end of that day, that's their decision to make."
Netball Australia CEO Marne Fechner praised Alexander's time with the team but said there was an "appetite for change".
"Lisa has had a significant impact on our sport and achieved great things in her time, both on and off the court. She is leaving a great legacy," Fechner said in a statement.
"As we looked to the next high-performance cycle and beyond, there was a consensus and appetite for change heading into 2021.
"The high-performance landscape is ever-changing and increasingly competitive and we believe it's in the best interest of the program to open up the role."
Netball Australia will begin their search for the next coach early next month.