I've also been able to buy non-knock off batteries for just about all electronics up to a few years ago when companies decided that soldered in batteries shorten the time-to-landfill of their products improving their revenues.
Seriously: there is no reason why there could not be a standard form factor for battery cells. If we can do hard drives, CPUs and RAM I'm sure we can do batteries too.
Most people don't know how to choose a proper hard drive compatible with their M.2 adapter or cable for their USB device. Many people also buy counterfeit USB sticks and SSDs that don't have near the capacity they advertise. You and other tech-literate people aren't the only consumers manufacturers are selling to. Nor are people always sufficiently educated, or living among stores with sufficient reputation to source from a reputable aftermarket vendor for their replacements.
If I could do it at 6 and my mom can do it at close to 80 then I really don't see why other people could not. Sometimes there just isn't a problem unless you make one. Standardize the cells, sell them through the supermarket chains at a normal price, just like Duracell and other quality battery manufacturers have been able to do for ages. Problem solved, once and for all. No need to go through AliExpress, Amazon or some other shady online store, if you are that concerned about trust then the only way to solve that is to buy from a reputable vendor.
See also: vacuum cleaner consumables, independent car repair
It would also make it easier for people to learn how to replace batteries.