You're the one who assume that.
Vegeta doesn't instantly becomes an earthling, he adapted and bonded with them. He married an earthling and conceived a child. Those bonds showed him emotions, and he accepted that earth is his home now.
Which has nothing to do with gaining an ability that was claimed to be a earthling trait in this thread. But we are arguing in circles so ima bow out
I put my heart and soul into my work and I fear I have lost my mind in the process