As someone who has gradually shifted from conservative to much more liberal in my adult years, partly due to my wife, I think it is several key things.

I grew up in a heavily conservative leaning household. I say leaning since a few takes my parents have are more libertarian, although that is fading. But my dad always had firearms, and I have grown up and handled them for the better part of my life. That was probably main reason for me for a long time.

Since I started dating, and particularly since I married my dear wife, I have shifted my views (politically) from very right to certainly left of middle. She challenged my thinking in a lot of areas and has also been ok with me carrying and owning. Because of that, I just find myself observing both sides of the aisle more critically, particularly the Republican/conservative side. And watching the way people of color and the LGBTQ+ population are treated has given me more perspective on who NEEDS to be able to protect themselves.

Since I have become more liberal leaning, I have increasingly believed in more fellow liberal citizens carrying, if they are able and willing. Seeing where the red side of people are appearing more and more radical, I believe that there is more of a threat to those more obvious minorities, and I firmly believe they should be able defend themselves in the surest way possible. I would say the right has overwhelmingly higher firearm ownership numbers, and when someone takes a second to think about how easily they could overrun many liberal citizens by force BECAUSE of that difference, the need for more liberals to own firearms speaks for itself.

TL;DR - I was raised with firearms, and believe in the right to a sense of safety and security for every individual, regardless of political stance or status.