Well you should - the fact they're pretty much electrically identical means that you can confidently buy off-brand batteries if they have good cells and that adapters can be possible.

I think you're missing the point focused on your point. We all understand the internals are probably coming from the same factory line. The problem is that they don't connect universally. As someone up the chain elsewhere stated, if the markets can be forced to use the same USB charging port, there should be a similar regulation for these kinds of things as well. Whether that's a universal battery shape/connector for tools, eBikes, whatever. We've unified things like 110v mains plugs, 220v mains, etc.

The fact that they do all use the same internals makes this even more egregious.

The internals are completely interchangeable. You'll even find the same model with different internals.

I agree with you 100% about the need for regulation.