People are being true to themselves and walking away from something they don't believe or something that has left them because they can't fit the right mold. If someone if a young man or woman who is gay or lesbian, the church teaches that the only we for them to be accepted is a lifetime of celibacy.  And those that have been badly hurt by abuse and have been brutalised in Catholic institutions can not be expected to want to stay. It wasn't Catholic teaching that drove them away, it was abuse.  
My parish is thriving, it is fairly liberal and people that are remarried at welcome too, even if they don't take Communion.  And they give a lot to Parish life. I attended a funeral today, the idea of the mention of Purgatory would have been insulting if it happened. Especially when people often have dementia at the end of their lives, but have been devout all their lives.