Hi!
I write in first person, so I am probably well-placed to answer.
I have to say I often land in first person after trying third and realizing it just doesn't work for the story.
I write YA, which is generally considered a natural fit for writing in first person. My stories tend to be personal journeys, rather than action or adventure, so first person allows me to show the full breadth of the journey by revealing the inner workings of the protagonist's mind. There are ways to achieve this with third person, but I find first person more immediate and therefore more effective for me, at least. My stories also tend to have an element of mystery and I find that telling the story in first person means the reader can only know what the protagonist knows and therefore are forced to undertake the same journey as the main character.
I agree that this can create difficulties with the reader in terms of connecting - especially if they are worlds apart from the protagonist.
I hope that gives some insight into at least one author's reasons :-)