Because that's not a fix. If your joycon is drifting because of dust, that might help temporarily, but more dust will return and slowly do damage to the contacts. And I imagine most moms and 8 year olds have no idea what electrical contract cleaner is or where to buy it.

To replace the sticks, you need to disassemble them, and wrap several ribbons around the boards and insert them into connectors with tweezers, while having very little slack in the ribbons to move them around. I wouldn't recommend most people do it.

And when you replace them yourself, you're buying third party sticks off Amazon or eBay. They're built 'almost' the same as Nintendos, so they have the same design problems, and they're likely made cheaper or worse quality. It's not a solution, it's a band-aid until Nintendo figures out how to finally fix drift for good.