The most important reason is profit reduction — both long and short term. Hotswap sockets cost a little bit more per keyboard. Most mass market keyboards are incredibly cheap to make, and produced in batches of several thousand or more, so companies don’t like the added cost eating into their profit. They also make repairs very easy; when switches wear out people are much less likely to buy a new keyboard instead of doing the repair themselves.
Hotswap sockets also require some engineering expertise to implement. They take up extra room on the PCB so component placement and routing must be precise. This limits international layout support at the PCB level, especially if a keyboard has LEDs. If you want a European enter key or split space bar for a hotswap keyboard, separate PCB designs are usually necessary. Keyboards like the Minivan, which is no longer available, achieve partial all-in-one success by reducing LED functionality.