Im contacted by recruiters via LinkedIn literally on a daily basis for senior positions. But I never get a reply by google even though I applied there like 10+ times already and fulfill their basic requirements. I never wrote an application letter (because they say it’s optional)
They care about the same things most companies care about: diversity, prestige of your school, your social status, your looks, your published research, your grades, your open source contributions, your internships and work experience. At the end of the day there's some things you can do, but there will always be some things outside your control.