PTSD is not something people easily just go find help for. It takes a support system. It's a serious disorder and often times not even properly diagnosed until it's too late. Some people think they can deal with it on their own. Sometimes yes, often times no. But it's like most things internal.
Think of losing someone close to you. If someone tells you to just get over it and carry on, is that even a remote possibility for you?
Same with PPD or other forms of depression.
The first step to actually helping someone is coming to terms with the fact that we don't all process trauma the same, especially neurologically. Sometimes no, they can't just seek psychological help on their own.