Where do you go to buy a plastic gear for a RC car? Identifying a matching part and getting it is a task that probably most of us have become incapable of. I also believe that much of the infrastructure that made repairing things like this easier in the past has disappeared to a large part.
There are hundreds of rc car parts sites, as well as robotics hobbyist shops, and industrial parts sites that carry generic plastic gears. If you insist on shopping in a brick and mortar store, of course it depends where you live. In my smallish city there's at least one surplus store that has many bins of small mechanical parts, including plastic gears. With the rise of the maker movement, there are more resources for things like that than there were even a few years ago.
If you are incapable of counting teeth or measuring things, I'm sorry, but most people could if they wanted to. And almost all people are capable of purchasing things online.
(That being said, some toys are now so cheap that it can be cheaper to replace than repair, especially if you have to pay shipping on the part but not the toy).
Then you need a way to get physically around the item (while it is still mounted, broken) to accurately measure it. Then you need a means to re-install it, repaired, after removing the old one. The fundamental truth is that it's significantly cheaper (and lighter, and uses less material) to design throw-away products at this level than to engineer removable elements to make them possible to repair.
Because you won't take the time to fix it! What a waste!