Mr Atkinson had been on the board for 19 years and delivered 17 consecutive surpluses, before handing the main financial role to Mr Druzianic who had delivered two.
Some have said the groups' resignations were not entirely out of the blue - at the Union's annual meeting in February, the four had raised issues about the organisation's leadership and "poor succession planning".
Yesterday Mr Atkinson said the union's constitution was "outdated" and "not fit for purpose" - which was highlighted by a dispute relating to the election of a new HBRU chairman.
When the agreement they reached with the current chairman Brendan Mahoney - to have board only time allocated at following board meetings to discuss succession planning - did not happen, this became the "straw that broke camel's back".
"We've resigned because we can no longer work in an environment where one of the key principles of good governance is not observed by the chairman of the board."
Had the situation been dealt with better "the issue could have been avoided, the issue of us all resigning could have been avoided"," he said.
HBRU chairman Mr Mahoney said he did not want to comment, other than with a statement he released earlier this week.
Mr Tremain said he had resigned as he "felt we needed some change in leadership, we needed some succession planning, and we needed some new faces, new younger faces a female face on to the board".
"I felt we needed a bit more transparency over some issues...and I was concerned about the extra funding we'd got last year and our final profit loss."
He added he had hoped to see a wider involvement, and communications between the union, and clubs and schools.
"Nobody's going to be happy with every decision that's been made but provided they've been given very opportunity to be consulted, and given a voice, and then a decision's made everyone moves on in the game's best interests for everybody."
Now, Mr Druzianic said he and Mr Atkinson were calling for a comprehensive review of the union's constitution, and were urging clubs to "rally together and get into action and get some positive outcomes from here on".
The four felt their actions could generate positive change for the union, he said, and he hoped the board would be encouraged to carry on discussion around succession.
"We think there should be a limit to the number of years board members need to rotate off the board and that's the sort of thing I'd be hoping clubs would be coming back to the union in a constitutional review."
When asked what he thought would happen if the union did not take on the feedback, Mr Druzianic said the clubs could demand changes, or a worst scenario, could propose a vote of no confidence in the remaining board members.
"But you'd hope that they'll all have a constructive conversation and make some changes and carry on."
When asked, Mr Randell said he did not think the union would take heed of the message sent by the quick resignations.
"There's four directors gone...you'd think they might have a bit of alarm," he said. "Brendan [Mahoney] said 'the union had been in place since 1884 and it will continue on. We've had some directors who have tossed their toys, and new directors will be elected'."
"[Does that sound] like a chairman, or a board that's going to take heed of what's going on? Their comments are it will continue on."
Mr Randell said he was disappointed to have had to resign, "but there was no option".
"This is not a knee jerk reaction, people say you should have stayed on there and [tried] to affect change, we've been trying to do this for a number of years and we've been told pretty much flatly go away".
The four resignations has allowed for new faces on the board - the union have called for a special general meeting, and are now working with clubs to fill the vacancies "as soon as possible".
Mr Mahoney said that although he could understand the exits of Mr Tremain and Mr Randell "following the failed attempt to take over the board", the reasons given by the other two directors for their resignations relating to governance and change "just did not stack up".
"The union is in a very strong position, and this is a result of excellent governance, including by the exiting board members. The financial and structural fundamentals of the union are all sound. Rugby in the Bay is in very good heart," he said.
The chairman had met HBRU life members and past presidents who had "confirmed their strong support" of the board, and staff, and had "expressed serious concern at the actions taken by the board directors who have resigned".
The chairman said they were now looking to fill the four vacancies.
"Indications are that our clubs are going to nominate excellent candidates with a diverse range of skills and experience and the time to devote to make a full contribution for the good of the game of rugby in Hawke's Bay."
Mr Mahoney said he would not comment when asked whether the union would take on the message sent by the four resignations.
HBRU chief executive Mike Bishop did not return requests for comment.
Immediate past chairman Richard Hunt said he could not comment on the matter, other than to say that the union would now be working to appoint new directors.
Mr Atkinson added the four departed directors were still positive about Hawke's Bay Rugby, and had not wanted to damage its brand, or have any negative effect on the organisation by resigning.
"We've spent a hell of a number of years getting the organisation into the financial state it is now, it would be terrible if that was damaged but it just reached a point," he said.
He said the union's feelings appeared that the organisation had been around since the 1800's, and had "done ok, so we'll carry on".
"What I've seen, my experience has been organisations with that attitude are heading for a bloody big train crash."