Explaining a move away from your old field

Why do you want to leave the area you have been working in until now?

Frame it as moving toward something, not running away. Explain what attracts you to quantitative finance (applied problems, markets, faster impact) and how skills from your previous field carry over, while staying positive about your past work. Avoid criticising your old field, supervisor or employer; interviewers want to see a considered decision and long-term commitment.