for as many people there are in the world there are reasons why some of those people don't get help. Some of those reasons are -

lack of money to pay for it.

Don't air laundry in public type raising and family values.

the abused children taught to "keep their mouths shut or else" grow up to be adults who live in fear of the "or else" should they try to get help.

Societys views that any one who needs a therapy professional is crazy so they don't want to be thought of as crazy.

mass media's special FX and overdramatized portrayal of therapy and various disorders sometimes scares them.

Personal experience of getting help and ending up locked in some mental health unit so the person avoids anything that will result in that happening again.

Some of the people who don't get help do not realize they have a problem - in the psychological field there is a saying - The insane think they are just fine and the sane think they are in sane or going insane - this is because with some disorders they have always been that way so they think that way is completely normal and think everyone is like this until they are told otherwise.