With Guerra flagging legal action, Smith would not go into any detail about why the AFL club made the change only seven months after he started as head.
Tuesday's sacking also came a year to the day that the Demons announced the former Victorian chamber of commerce boss had won the role.
Veteran club administrator Brian Cook, who had been mentoring Guerra at Melbourne, was appointed interim club chief until Taylor takes over in about three months' time.
On Wednesday, Smith revealed Guerra's sacking had been orchestrated "a week or two ago" when Taylor and then Cook were approached.
"There was no one, particular, thing - it was just a general lack of confidence," Smith said, also confirming it was a unanimous board decision.
"Probably in the last couple of weeks, it came to a head.
"We needed to have a Plan B in place, to make sure. It was a difficult decision for us to make."
Smith acknowledged the chaos and confusion on Tuesday around the sacking.
"We could have been clearer on the messaging and we weren't on that. But by the end of the day, I think the messaging was clear that it was this lack of confidence and breakdown of (the) relationship," he said.
Smith would not be drawn on a media report that the club had been concerned about an alleged link that Guerra has through horse racing.
"That is something I will not be providing any specific details on," Smith said.
Taylor already sits on the club's board as a non-executive director.
Smith said Taylor boasted experience the club needed, with the incoming chief executive overseeing Stan Entertainment and Stan Sport in his role as executive director at the streaming service.
While the team is thriving on the field this season under new coach Steven King - currently sitting fourth on the ladder - Guerra's sacking continues the off-field dramas at Melbourne.
They are yet to secure a new home base at Caulfield, although Smith said they are "very close".
They had an interim president and CEO for much of 2025 and that proved a factor in the sacking of former coach Simon Goodwin.
Smith is also the club's fourth president in the past six years.
Standing next to Smith at the media conference, Cook said Guerra was the latest in a string of club chiefs without football experience who had not succeeded.
Now the Demons are replacing him with Taylor, who also has no club experience.
"There are very few CEOs who come from outside football, into football, and become successful CEOs in footy," Cook said.
"It's a difficult task to understand the footy culture.
"This one is a bit unfortunate - I feel for Paul, he's a good man. But footy has a strange way or working sometimes."
But Smith lauded Taylor's skill set and was confident he would succeed in the role.
"He will be a great replacement CEO," Smith said.
"Sometimes you get one wrong, and we think we just got this one wrong."
Asked about Guerra potentially taking legal action, Smith said "so be it".
"He was aware of my dissatisfaction on certain things, but yes, I accept he was puzzled by the decision."
Smith said it was a "strong, hard" decision to sack Guerra now, rather than wait to the end of the season.
Guerra was integral in Melbourne's decision to appoint King as a replacement for 2021 premiership coach Goodwin, who was sacked last August.
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