For some of us it's more than a few dollars. I paid $300 at LensCrafters for my sons glasses which broke within a few months, and only $24 for glasses online and they are great- sturdy and well made
I don't think it's a matter of the glasses being sturdy and well made; it's a concern of them not fitting properly. When you get your glasses in person, they measure your eyes, the space between your eyes, etc etc etc. You can't possibly do that online and if your glasses aren't measured properly and the lenses aren't in the proper place, you can do more damage to your eyes and make your vision worse (among other things).