Why people mute swear words in movie promos?

[Candle]

Because if they don't, I will hesitate to share it with my loved ones or family members, even if it was great and I wanted to share it badly. 

[integral]

Normally there's a rating system and you want to keep things PG-13 to make it accessible to a wide audience to get as many sales as possible. A movie with excessive swearing will alienate a portion of the audience, So a business minded person is trying to capture the largest audience.