Try it. Move your Steam window around. See how it snaps to the edges of your display(s)?
Why is Steam the only program (I know) that does that natively? I would love for ALL my Windows programs to do that (without installing 3rd party softwares/scripting).
EDIT : I’m on Win10.
Don’t worry friend. I know exactly what you’re referring to and I wish it was more common as well. I hate having to use that bit of brain power to appease my OCD and have the window be perfectly aligned to whatever edge I push it up against.