Is sci-hub also used in places having institutional access? Has there a study been done regarding the issue? Because I've seen a lot of people directly pasting the doi at scihub without even checking if our institution library wifi has access to the particular journal (even when they are right in the lib).
The only study that I'm aware of is the magazine article that Orion linked to in the comments. Anecdotally, however, my experience matches yours -- even in places with institutional access, some people prefer sci-hub as it's quicker and easier. No need for a lab-specific login or password, no need to check if the journal is actually one that your institution subscribes to; just paste in the DOI and go. In fact, there are even web browser extensions that automatically append the sci-hub URL to the page you're visiting, so with a few keypresses you can be automatically forwarded to sci-hub's cache of that page.