Because people grow up in religious environments which result in many of there friends and beliefs being tied to that religion. People only stop believing when they are faced with undeniable evidence (which for most is impossible because religious teachings are unfalsifiable) or more often when there is an emotionally charged conflict between there religion and another part of a persons’s life.
For an example of the latter, I once knew someone who started questioning (and eventually became agnostic) because the church they had always went to had started preaching homophobic messages which was irreconcilable with there closest friend being gay.
Sneakernet is getting worse and worse these days, I’m learning the ancient art of astroprojecting into random people’s rooms to consume media.