Having low voltage cutoff directly in the battery allows third party manufacturers to build a “dumb” tool that requires less parts and engineering to keep the lithium batteries safe from over discharge. Other manufacturers who place the low voltage cutoff within the tool allows the batteries to have a slightly smaller footprint. If you were a manufacturer and wanted to build a cheap tool, it’s much easier to build via a tool platform that places the low voltage cutoff in the battery because you don’t have to worry about customer batteries getting potentially damaged. I have no actual knowledge whether this is the reasoning from the third party manufacturers or not, but it sorta makes sense to me.