I have several objects on my desk made of glass with rounded corners. The glass lunch container I ate out of a little bit ago. A squircle glass bowl on my desk holding various nicknacks. The glass on the front of my phone. The glass I'm drinking out of right now has rounded corners. I used to have a kitchen table that had the top as one giant sheet of glass as a square with rounded corners. The windows in my car have some corners rounded. Tons of glass things have rounded corners.

Rounded corners is easier than straight. When you work glass, its usually somewhere between a liquid and non-Newtonian fluid. Molding it into round frames is trivial.

That's why we have round glass coasters, round lenses, round glasses for drinking, etc.

Almost every common glass object I can think of has rounded corners. The only obvious exception is most household window panes. I have to think pretty hard to come up with another one...maybe aquarium tanks? Some mirrors and glass tables, although the images that comes to mind for those are just as likely to be round as square.

I'm very curious which items you went through before concluding that glass almost never has rounded corners.

The fate of all perfectly squared glass sheets is to become quite round if you get them hot enough. If you get a moment, try looking up glass fusing. It is admittedly a niche hobby, but it's pretty interesting what starts happening when you apply a little heat.