Those who think that pulling in forward is easeir and quicker then backing in must be living in places where the lanes and parking spots are pretty wide.
Apart from the added safety, as explained by others, you keep your manouivrability when backing into a spot, making parking in a tight spot easier. I regularly park in places where pulling in forward is not possible or difficult, but backing in is a quick and easy manoeuvre.
As an example of what I mean, when the space you parki in is just wide enough to get out of your car, then you have to be almost completely lined up with the spot before your front wheels go between the cars to your side. When backing into a spot, you can still manoeuver a lot with yopur front when you are between the cars, meaning that you have to be less lined up when getting between the other cars. Due to this, you can then park with smaller lanes as well.
I do think we have often have smaller spots here then in the US, but most people back into a spot anyway, regardless of how much space they have.
As for the pulling in and back, this happens both with people backing in and with people pulling in forward. A good reason why people backing in may do it a bit more is also that, due to above mentioned reasons, it is actualy easier to cerrect their position with a quick out and in, then for the person pulling forward, and it is also safer to do this for them.
I would like to point out, that I think that in daily live I see more people backing in then pulling forward here (anecdotal, but I just stepped out and there are at the moment 15 cars parked in my street, 4 forward and 11 back.) Apart from the more often tight spaces, another major difference with countries where many people posting here come from is that over here only professionals are allowed to teach people to drive, and they will teahc you to park (both perpendicular and paralel) by backing into a space.