[oliwarner]

Capitalism.

Let's not waste a thousand words when one will do. It's really that simple.

All these batteries are just 18/36/54 Volt configurations of 18650 cells (with a few exceptions). Some have $0.50 undercharge management chips, some don't. The difference is the mounts and pinouts and they are only distinctive to avoid interoperability.

They do this to keep you brand-loyal.

As soon as you buy a kit (eg driver, drill, battery and charger) for a knock down rate you're much more likely to buy other "bare" tools from the same range because they're compatible with the expensive battery you've just bought. It's cheaper to stay loyal. As soon as you go pro, that loyalty is magnified because you need multiple batteries ready to go. Owning and charging that redundancy across multiple platforms is a lot of overhead.

They could all use the same batteries and chargers. They choose not to.

Bosch has made a common platform (now called AMPShare?) but the buy-in is limited (mostly smaller, mostly German toolmakers) and Bosch seems to do best out of this, but it's a start.