>>281881560
It didn't really. Vegeta believed Super Saiyans were invincible, which was the reason behind a lot of his behavior in the Cell arc compared to Frieza, but he didn't really change that much.

He died, learned that Goku is a legendary super warrior, avenged his planet’s destruction, and his boss got blown up twice. That tends to change something.

>>281881560
He was genuinely proud that Goku became a super saiyan and defeated Frieza, because it affirmed his race's superiority, and thus his own superiority that he belongs to a race that produces Super Saiyans. This mindset allowed him to either mellow down out of respect for Goku's feats, or found himself lost and purposeless because HE wasn't a super saiyan. Regardless of anything else, he now knew it was achievable, and slaughtering goku's friends wasn't exactly a step in the right direction to getting him there. Goku grew up on Earth, so he likely had a desire to stay there during his "directionless" period hoping something would open his eyes to the path of a Super Saiyan, since it's the planet Goku is from. Frieza's return likely angered Vegeta greatly because he was still inferior to Frieza's strength, so from that point onward he found his purpose and trained x10 harder for the sole purpose of becoming SSJ, having no desire for anything else including petty slaughter.

Bulma

If he's such a prideful Saiyan why did he never regrow his tail?
Isn't he like the only guy who can fully control his Oozaru form.

>>281881560
Bad writing. He became completely flanderized.

>>281881560
The writer decided it should.

Sorry but i didn't watch the show

He became too prideful. Namek arc Vegeta knew his limits and how to try and break them but also how to backstab his opponents.