Conte resigned from his post as Juve boss on Tuesday just months after winning a third consecutive league title with the club.
And Moggi said he was surprised by the 44-year-old's departure, adding he has no idea why he left the club.
"The news surprised me. I tried phoning him, but he didn’t answer," Moggi told Tuttomercatoweb.
"I don’t know what happened. I'm sure he didn’t do it because of an offer from another club. I think he’d always choose Juve first, so it must be painful for him to take this step."
When asked if he felt Conte resigned over the possibility that Arturo Vidal might depart to join Manchester United, the 77-year-old replied: "It could be, but with an offer worth €50 million you need to take it and find replacements.
"Clubs must look at the balance sheet, as nowadays we see bankrupt clubs all the time and budgets must go hand in hand with sporting requirements.
"How will Juve do without Conte? The King is dead, long live the King. Coaches come and go."
Moggi was then asked if he thinks Conte could take over the Italy national team, but he said he would "rule that out".