Funny Valentine: see above
Diavolo: “I have spent the entirety of my life in anonymity. No one knows who I am so I’m untouchable. And while I made a mistake in the past, I’m using my chance to correct it
Pucci: “One of my only friends and the guy I am possibly gay for had died. He had a dream of obtaining heaven. And I’ll be damned before I allow his dream to be all for naught.”
Kira: “I’m honestly just a normal guy and I just want to be a normal guy. Though I have been spoiled from birth by my parents. I also have a hand-fetish so I’m also a sick-minded serial killer”
Kars: “I have sought hard to overcome the only weakness of my people and become the best that there is! I had to kill most of my kind because they could not understand the good I could do for them. I’m close to a breakthrough but I JUST NEED A PERFECT STONE!”
Human Dio: “I have grown up in such a run-down area of England I’m surprised it wasn’t named ‘Suicide Slums.’ I grew up disrespect under the worst father ever who worked my mother to death. After I gave him his just desserts I got adopted into the Joestars as part of an ‘inheritance.’ I intend to become the successor of that family so I can reach the top, not be disrespected ever again, and give the ultimate middle finger to pops.
Vampire Dio: “LOL! Look at those LOSERS with ‘Motivations!’
Human Dio: “You’re me!”
Vampire Dio: “Yeah. WHEN I WAS A LOSER!!!”

Arguably Kira's motivation is one of the reasons why I like him as a villain so much; the contrast between his mundane worldview, motivations, and lifestyle and his psychopathic nature make him a compelling villain for the sheer uniqueness of it. He's kinda like a suburban Patrick Bateman, and a dark twist on "relatable" characters before "lolsorelatable" really entered the public eye.