Marshall unsuccessfully sought a trade to the Cats last year when St Kilda recruited Tom De Koning as their No.1 ruck.
But a deal could not be struck and the "shattered" ruckman had to return to the Saints, before putting in a fresh trade request this year.
After plenty of posturing from both sides, Geelong on Thursday paid up this year's first-round selection, currently pick No.14, for Marshall and St Kilda's 2028 third-round selection.
It followed Marshall choosing not to attend the Trevor Barker Award on Monday night, news of which broke earlier that day.
"I had no idea it would blow up like it did, to be honest," Marshall said on Friday.
"And reality is I just didn't feel comfortable at the time."
Pressed on why, Marshall said: "Oh, just a few different reasons, but just didn't feel comfortable, probably having a lot of interactions with a lot of people."
Asked whether he'd spoken to Lyon or football boss Lenny Hayes, Marshall, who was adamant he'd left St Kilda on good terms, said: "Not yet.
"I spoke to Lenny a little bit yesterday, but yeah, I'll speak to Ross in the next couple of days."
The ruckman was playing golf when the trade went through.
"(My game) was all over the shop the first five holes, and then got the message from Dave Trotter, my manager, and he said, 'Congratulations mate, you're a Cat'," Marshall said.
"And then (that) freed up the swing a little bit and went on a pretty good patch from there."
Marshall is joining Geelong with fellow boom recruits Toby Greene and Jordan Ridley.
He is adamant his best football is ahead of him and he can play with talented young ruckman Mitchell Edwards, 21.
"I think it's going to work really well. I think we hopefully complement each other really well," Marshall said.
The 30-year-old crosses to the perennial flag-contending Cats after their season ended with a gallant 14-point semi-final loss to Fremantle at Perth's Optus Stadium.
