If Toyota thought it fit within their business model and they could make money off of it, they would 😉
That's the bottom line, companies believe the marketplace has not reached saturation and so they're jumping in. Personally I do think its at saturation and at some point we'll be seeing a shake out of the less financially strong makers.
Carriers have only certain amount of space to carry phones, and consumers don't want to be buried by an overwhelming number of choices. I can't speak to Kyocera, but I only look at a handful of makers when choosing my phone. Apple, HTC, Samsung and if the Nexus model (who ever is the maker of the current flavor)