Speaking to the media during a conference call on Monday, Blues GM George Armstrong confirmed the team's decision, which was strengthened by their ability to re-sign goalie Brian Elliott.
"Brian will team up next year with Jake Allen to provide our goaltending tandem. We're looking forward to those guys competing and performing well," Armstrong said.
"At the trade deadline, we took a calculated gamble of bringing in Ryan and we didn't have the success that we needed as an organization; certainly not all reflective on Ryan. It's a team game."
Elliott, 29, signed a three-year, $7.5 million contract earlier in the day.
Armstrong also indicated that part of his decision that factored into not to re-signing Miller was that the Blues would have had to give the Sabres additional assets.
"There were additional payments necessary to Buffalo if we signed Ryan," Armstrong said. "That would've been moving back a full round in the Draft from the first to the second round and adding a third-round pick, and we just felt at this time that it was better for us to go with Elliott and go with Jake Allen."
Armstrong met with Miller after the Blues were eliminated from the playoffs in the first round and spoke to him against last week.
The Blues are expected to pursue a top-six forward this off-season, though Armstrong indicated that he wants to make a "good, calculated business decision" that fits under the salary cap.