Because unifying everything down to a single one dumbed us down and gave unwarranted control to fewer and fewer people on what we may listen to, what we may write, what we may photograph, what we may share. And how and where and why we do it.
(notwithstanding that this would allow to significantly enrich the affordance of each device/appliance, relative to its use, rather than just having everything only tactile on a screen made of glass and 2 buttons).