It's not even about a product category. It's about control of the surface area of interfaces people use. Interfaces that aggregate other services often hang poorly, but if you can build one people seek to use, you can build a brand (a name bound to positive connotations), which becomes a durable and valuable position to control. Mental real-estate in mass awareness is hard-won.

Voice control today is somewhere between gimmick and strictly dominant, depending on the situation and provider. If you consider the trends of interface design from line console to GUI to touch, each used newly-sophisticated tech to become more broadly accessible. With this broadening the stakes go up. I think that explains the proliferation of speaker chatbot products; they are just one front in a larger competition for that space people interact with directly. That particular front may or may not turn out to matter in the long run. Concurrent battle sites are car integrations and streaming devices/USB-sticks for TV's. This is why these same companies keep showing up to the same battlefronts with more or less equivalent strategies (semi-shiny new interface tech that happens to funnel you into their marketplace regime); they all want to be your concierge at the ready, in order to steer economic activity.