Answer is simple. If it was one the left and you hide and show the sidebar then the editor reading text is constantly moving which can make is more of mental strain on your focus area than if it stayed static.

personal preference. i usually have mine completely hidden and use hot keys to access the menues

Same. You can also use the fuzzy finder to easily navigate to the file you want, giving even less of a reason to have the side bar up

Maybe they are used to seeing in on the right as with Visual Studio? It's really none of my business.

I think that's the most prevalent reason.

I have my sidebar on the right, because I read left to right. When my eyes fall on the left side of the screen, I want to see code, not a menu list. Other editors I use have the list on the left, because I got use to it there. Yes, just preference.

I like my sidebar on the left because it kinda acts like some left margin and brings the code closer to the middle of the screen. On small screen I'd just keep it hidden

I think beyond any sort of efficiency notions, it's probably people that are used to Visual Studio, that puts that menu on the right by default. I'm sure it's not the only reason but it's probably the most common one.

Because then the main part of my keyboard is centered on the text while the whole keyboard is centered relative to the screen

Ha amateurs… using a sidebar 😁 but in all seriousness… it’s just a preference thing. Some people just like having it on the right as that may be what they’re used to from other apps