During boarding, it is often possible to put stuff in the overhead bin while standing in the aisle seat area if no one is sitting in the aisle seat yet, leaving the aisle free to allow others to go by.
But most people stand in the aisle when putting stuff in the overhead bin, even when the aisle seat is unoccupied, blocking the aisle. Why?
I have had people take the overhead bin I had targeted when I stepped aside to adjust and put my own bag in. If I had stayed where I was and blocked their access I could have gotten my targeted space as I was in the line in front of them. Also I find it somewhat of an awkward angle to put a 20"+ bag into the overhead bin while standing in the aisle seat area. For me it's so much easier if I am directly in front of when lifting my bag up. What works for you doesn't work for all.