There are many reasons the Cavaliers elected to fire head coach David Blatt, but overall team success couldn't have been one of them. The Cavaliers were on pace to easily win the Eastern Conference and finish with exactly 60 wins. That's the best winning percentage of any coach ever fired in the middle of the season.
David Blatt is 1st NBA head coach since conferences began to be fired when his team has best record in its conference. (via @EliasSports)— SportsCenter (@SportsCenter) January 22, 2016
The Cavaliers' record is even more impressive when you consider the team's injury situation. They amassed a 30-11 record despite three of their five normal starters struggling due to injury. All-Star Kyrie Irving missed the season's first 24 games with a knee injury dating back to last year's Finals, while starting shooting guard Iman Shumpert missed 22 games due to a fractured wrist. Center Timofey Mozgov has returned slowly due to a knee issue of his own and lost his starting spot to Tristan Thompson, who himself arrived late to training camp as he negotiated a new contract. Given those issues, it's impressive the Cavaliers have such a great record.
Nevertheless, it's clear the team has pondered replacing Blatt ever since LeBron James decided to return to Cleveland in July 2014. Players did not appear to trust Blatt, and James has always had an awkward relationship with him. Rather than wait any longer, the team elected to make the move now.