how to find a niche or theme for personal statement?

every time i read a personal statement that got into oxbridge or lse or kcl or whatever they always seem to have a niche that they talk about. for example for cs it may be llms or microships or the ethics of ai and for law it's women in the justice system or immigration

as someone who wants to study philosophy politics and law i thought yeah this is a good idea but i'm finding it hard to find a niche i can deep dive into and i believe the topic you focus on also affects supercurriculars

so i'm just stuck rn

how did you guys find your theme or topic to focus on?