Reina felt the time was right to leave Liverpool after returning from Spain's victorious 2010 World Cup campaign to find the Reds in chaos.
Rafael Benitez had been sacked as Liverpool manager, while director Christian Purslow was desperately seeking new owners to replace Tom Hicks and George Gillett as the club lurched into a financial crisis.
Reina, unimpressed by the decision to hire Roy Hodgson as Benitez's replacement, was ready to accept Arsenal's offer.
But Purslow insisted Liverpool should reject the bid because he feared the Spaniard's sale would discourage potential buyers from pursuing their interest in the club.
"I went from elation one minute to depression the next as the realisation dawned that Liverpool were going nowhere fast," Reina wrote in his new autobiography.
"When I signed my contract in April 2010 I hoped that better times were just around the corner, a feeling that was fuelled by the promises of improvement from people at the club.
"It didn't take me long to feel that their promises were hollow.
"I felt betrayed. Our owners were at war with each other, the club's debts were spiralling out of control and a change in manager had failed to dispel the feeling that we were on the road to nowhere.
"Arsenal had made their determination to sign me clear by offering £20 million, a phenomenal amount for a goalkeeper. Part of me felt that I was well within my rights to consider my future even if I did so with a heavy heart.
"When Liverpool received the bid, they rejected it. This was not because I had been told that I was too good a keeper to leave.
"The reason I was given was quite different - and it left me feeling down. I was told that my continued presence was crucial to the sale of the club. I was simply a bargaining chip in the sales process.
"I still don't know what to think of Purslow because I understand he was there to look for new owners and to try to sell the club but ultimately he was making big football decisions that he was not qualified to make."
Reina made no secret of the fact he wanted Hicks and Gillett out ahead of Fenway Sports Group's takeover of the club last October.
The 29-year-old admits he would have liked fans' favourites Steven Gerrard and Jamie Carragher to have joined him in getting behind the supporters' protests to oust the American owners.
"I was probably one of the loudest objectors because I believed it was important the supporters knew I was with them," he said.
"All I wanted the owners to do was sell up to people who could take the club forward, so I said so.
"The way I saw it, Stevie and Carra are the two principle members of our squad, the ones who the people love and if they had said something maybe it would have put Hicks and Gillett under real pressure.
"But in their view, it was more important to try to keep things as normal as possible."